Hi Thomas,

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 6aaf6d0abf39..6924d489a289 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -181,6 +181,7 @@ int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma) vma->vm_private_data = info; return 0; } +EXPORT_SYMBOL_GPL(fb_deferred_io_mmap);

/* workqueue callback */ static void fb_deferred_io_work(struct work_struct *work) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 84427470367b..52440e3f8f69 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1334,7 +1334,6 @@ static int fb_mmap(struct file *file, struct vm_area_struct * vma) { struct fb_info *info = file_fb_info(file);

• int (*fb_mmap_fn)(struct fb_info *info, struct vm_area_struct *vma); unsigned long mmio_pgoff; unsigned long start; u32 len;

@@ -1343,14 +1342,7 @@ fb_mmap(struct file *file, struct vm_area_struct * vma) return -ENODEV; mutex_lock(&info->mm_lock);

• fb_mmap_fn = info->fbops->fb_mmap;

-#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)

• if (info->fbdefio)

• fb_mmap_fn = fb_deferred_io_mmap;
  

-#endif

• if (fb_mmap_fn) {

• if (info->fbops->fb_mmap) { int res;

  /*

@@ -1358,11 +1350,18 @@ fb_mmap(struct file *file, struct vm_area_struct * vma) * SME protection is removed ahead of the call */ vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

• res = fb_mmap_fn(info, vma);
  

• res = info->fbops->fb_mmap(info, vma);
  

  mutex_unlock(&info->mm_lock); return res; }

• /*

• * FB deferred I/O wants you to handle mmap in your drivers. At a
  

• * minimum, point struct fb_ops.fb_mmap to fb_deferred_io_mmap().
  

• */
  

• if (dev_WARN_ONCE(info->dev, info->fbdefio, "fbdev mmap not set up for defered I/O.\n"))

• return -ENODEV;
  

If not configured - then why not just call fb_deferred_io_mmap(), as this seems to be the default implementation anyway. Then drivers that needs it can override - and the rest fallback to the default.

Sam

Hi Sam

Am 25.04.22 um 19:46 schrieb Sam Ravnborg:

Hi Thomas,

On Mon, Apr 25, 2022 at 07:26:32PM +0200, Sam Ravnborg wrote:

...

Hi Thomas,

...

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 6aaf6d0abf39..6924d489a289 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -181,6 +181,7 @@ int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma) vma->vm_private_data = info; return 0; } +EXPORT_SYMBOL_GPL(fb_deferred_io_mmap);

/* workqueue callback */ static void fb_deferred_io_work(struct work_struct *work) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 84427470367b..52440e3f8f69 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1334,7 +1334,6 @@ static int fb_mmap(struct file *file, struct vm_area_struct * vma) { struct fb_info *info = file_fb_info(file);

• int (*fb_mmap_fn)(struct fb_info *info, struct vm_area_struct *vma); unsigned long mmio_pgoff; unsigned long start; u32 len;

@@ -1343,14 +1342,7 @@ fb_mmap(struct file *file, struct vm_area_struct * vma) return -ENODEV; mutex_lock(&info->mm_lock);

• fb_mmap_fn = info->fbops->fb_mmap;

-#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)

• if (info->fbdefio)

• fb_mmap_fn = fb_deferred_io_mmap;
  

-#endif

• if (fb_mmap_fn) {

• if (info->fbops->fb_mmap) { int res;

  /*

@@ -1358,11 +1350,18 @@ fb_mmap(struct file *file, struct vm_area_struct * vma) * SME protection is removed ahead of the call */ vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

• res = fb_mmap_fn(info, vma);
  

• res = info->fbops->fb_mmap(info, vma);
  

  mutex_unlock(&info->mm_lock); return res; }

• /*

• * FB deferred I/O wants you to handle mmap in your drivers. At a
  

• * minimum, point struct fb_ops.fb_mmap to fb_deferred_io_mmap().
  

• */
  

• if (dev_WARN_ONCE(info->dev, info->fbdefio, "fbdev mmap not set up for defered I/O.\n"))

• return -ENODEV;
  

If not configured - then why not just call fb_deferred_io_mmap(), as this seems to be the default implementation anyway. Then drivers that needs it can override - and the rest fallback to the default.

Just to be clear - I already read: " Leave the mmap handling to drivers and expect them to call the helper for deferred I/O by thmeselves. "

But this does not help me understand why we need to explicit do what could be a simple default implementation. Chances are that I am stupid and it is obvious..

That's no stupid question. I didn't want to use a default implementation because there's no single one that severs all purposes. The current code all uses the same helper, but this will change with later patchsets. At some point, GEM is supposed to implement some of the logic for deferred I/O and will have to set it's own helpers. This can be seen in patches 8 and 9 of [1]. I think it's better to clearly fail here than to provide a default implementation.

Best regards Thomas

[1] https://lore.kernel.org/dri-devel/20220303205839.28484-1-tzimmermann@suse.de...

Sam

Hi Thomas,

a little ramblings below. Just my thoughts while trying to understand the code - especially since I looked at it before.

Sam

On Mon, Apr 25, 2022 at 01:27:50PM +0200, Thomas Zimmermann wrote:

Store the per-page state for fbdev's deferred I/O in struct fb_deferred_io_pageref. Maintain a list of pagerefs for the pages that have to be written back to video memory. Update all affected drivers.

As with pages before, fbdev acquires a pageref when an mmaped page of the framebuffer is being written to. It holds the pageref in a list of all currently written pagerefs until it flushes the written pages to video memory. Writeback occurs periodically. After writeback fbdev releases all pagerefs and builds up a new dirty list until the next writeback occurs.

Using pagerefs has a number of benefits.

For pages of the framebuffer, the deferred I/O code used struct page.lru as an entry into the list of dirty pages. The lru field is owned by the page cache, which makes deferred I/O incompatible with some memory pages (e.g., most notably DRM's GEM SHMEM allocator). struct fb_deferred_io_pageref now provides an entry into a list of dirty framebuffer pages, freeing lru for use with the page cache.

Drivers also assumed that struct page.index is the page offset into the framebuffer. This is not true for DRM buffers, which are located at various offset within a mapped area. struct fb_deferred_io_pageref explicitly stores an offset into the framebuffer. struct page.index is now only the page offset into the mapped area.

These changes will allow DRM to use fbdev deferred I/O without an intermediate shadow buffer.

v2:

• minor fixes in commit message

Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Javier Martinez Canillas javierm@redhat.com

---

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c b/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c index 02a4a4fa3da3..db02e17e12b6 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c @@ -322,12 +322,13 @@ static void vmw_deferred_io(struct fb_info *info, struct vmw_fb_par *par = info->par; unsigned long start, end, min, max; unsigned long flags;

• struct page *page;

• struct fb_deferred_io_pageref *pageref; int y1, y2;

  min = ULONG_MAX; max = 0;

• list_for_each_entry(page, pagelist, lru) {

• list_for_each_entry(pageref, pagelist, list) {

• struct page *page = pageref->page;
  

  start = page->index << PAGE_SHIFT; end = start + PAGE_SIZE - 1; min = min(min, start);

This is the same change in all deferred_io drivers like above. We now traverse pageref->list where pagelist points to the head.

It took me a while to understand that pagelist points to a list of fb_deferred_io_pageref and not a list of pages. I had been helped, had this been renamed to s/pagelist/pagereflist/.

If you see no point in this then just ignore my comment, I have not stared at kernel code for a while and is thus easy to confuse.

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 6924d489a289..a03b9c64fc61 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -36,6 +36,60 @@ static struct page *fb_deferred_io_page(struct fb_info *info, unsigned long offs return page; }

+static struct fb_deferred_io_pageref *fb_deferred_io_pageref_get(struct fb_info *info,

• 						 unsigned long offset,
  

• 						 struct page *page)
  

+{

• struct fb_deferred_io *fbdefio = info->fbdefio;
• struct list_head *pos = &fbdefio->pagelist;
• unsigned long pgoff = offset >> PAGE_SHIFT;
• struct fb_deferred_io_pageref *pageref, *cur;
• if (WARN_ON_ONCE(pgoff >= info->npagerefs))

• return NULL; /* incorrect allocation size */
  

• /* 1:1 mapping between pageref and page offset */
• pageref = &info->pagerefs[pgoff];
• /*

• * This check is to catch the case where a new process could start
  

• * writing to the same page through a new PTE. This new access
  

• * can cause a call to .page_mkwrite even if the original process'
  

• * PTE is marked writable.
  

• */
  

• if (!list_empty(&pageref->list))

• goto pageref_already_added;
  

• pageref->page = page;
• pageref->offset = pgoff << PAGE_SHIFT;
• if (unlikely(fbdefio->sort_pagelist)) {

• /*
  

•  * We loop through the list of pagerefs before adding, in
  

•  * order to keep the pagerefs sorted. This has significant
  

•  * overhead of O(n^2) with n being the number of written
  

•  * pages. If possible, drivers should try to work with
  

•  * unsorted page lists instead.
  

•  */
  

• list_for_each_entry(cur, &info->fbdefio->pagelist, list) {
  

• 	if (cur > pageref)
  

• 		break;
  

• }
  

• pos = &cur->list;
  

• }
• list_add_tail(&pageref->list, pos);

+pageref_already_added:

• return pageref;

+}

+static void fb_deferred_io_pageref_put(struct fb_deferred_io_pageref *pageref,

• 		       struct fb_info *info)
  

+{

• list_del_init(&pageref->list);

+}

/* this is to find and return the vmalloc-ed fb pages */ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) { @@ -59,7 +113,7 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) printk(KERN_ERR "no mapping available\n");

BUG_ON(!page->mapping);

• page->index = vmf->pgoff;

• page->index = vmf->pgoff; /* for page_mkclean() */

  vmf->page = page; return 0;

@@ -95,7 +149,11 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) struct page *page = vmf->page; struct fb_info *info = vmf->vma->vm_private_data; struct fb_deferred_io *fbdefio = info->fbdefio;

• struct list_head *pos = &fbdefio->pagelist;

• struct fb_deferred_io_pageref *pageref;

• unsigned long offset;

• vm_fault_t ret;

• offset = (vmf->address - vmf->vma->vm_start);

  /* this is a callback we get when userspace first tries to write to the page. we schedule a workqueue. that workqueue

@@ -112,6 +170,12 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) if (fbdefio->first_io && list_empty(&fbdefio->pagelist)) fbdefio->first_io(info);

• pageref = fb_deferred_io_pageref_get(info, offset, page);

Compared to the old code we now do all the sorting and stuff without the page locked, which seem like a big change.

• if (WARN_ON_ONCE(!pageref)) {

• ret = VM_FAULT_OOM;
  

• goto err_mutex_unlock;
  

• }
• /*
  • We want the page to remain locked from ->page_mkwrite until
  • the PTE is marked dirty to avoid page_mkclean() being called

@@ -120,47 +184,17 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) * Do this by locking the page here and informing the caller * about it with VM_FAULT_LOCKED. */

• lock_page(page);
• /*

• * This check is to catch the case where a new process could start
  

• * writing to the same page through a new PTE. This new access
  

• * can cause a call to .page_mkwrite even if the original process'
  

• * PTE is marked writable.
  

• *
  

• * TODO: The lru field is owned by the page cache; hence the name.
  

• *       We dequeue in fb_deferred_io_work() after flushing the
  

• *       page's content into video memory. Instead of lru, fbdefio
  

• *       should have it's own field.
  

• */
  

• if (!list_empty(&page->lru))

• goto page_already_added;
  

• if (unlikely(fbdefio->sort_pagelist)) {

• /*
  

•  * We loop through the pagelist before adding in order to
  

•  * keep the pagelist sorted. This has significant overhead
  

•  * of O(n^2) with n being the number of written pages. If
  

•  * possible, drivers should try to work with unsorted page
  

•  * lists instead.
  

•  */
  

• struct page *cur;
  

• list_for_each_entry(cur, &fbdefio->pagelist, lru) {
  

• 	if (cur->index > page->index)
  

• 		break;
  

• }
  

• pos = &cur->lru;
  

• }
• list_add_tail(&page->lru, pos);

• lock_page(pageref->page);

-page_already_added: mutex_unlock(&fbdefio->lock);

/* come back after delay to process the deferred IO */ schedule_delayed_work(&info->deferred_work, fbdefio->delay); return VM_FAULT_LOCKED;

+err_mutex_unlock:

• mutex_unlock(&fbdefio->lock);
• return ret;

}

static const struct vm_operations_struct fb_deferred_io_vm_ops = { @@ -186,15 +220,14 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_mmap); /* workqueue callback */ static void fb_deferred_io_work(struct work_struct *work) {

• struct fb_info *info = container_of(work, struct fb_info,

• 				deferred_work.work);
  

• struct list_head *node, *next;
• struct page *cur;

• struct fb_info *info = container_of(work, struct fb_info, deferred_work.work);

• struct fb_deferred_io_pageref *pageref, *next; struct fb_deferred_io *fbdefio = info->fbdefio;

  /* here we mkclean the pages, then do all deferred IO */ mutex_lock(&fbdefio->lock);

• list_for_each_entry(cur, &fbdefio->pagelist, lru) {

• list_for_each_entry(pageref, &fbdefio->pagelist, list) {

• struct page *cur = pageref->page;
  

  lock_page(cur); page_mkclean(cur); unlock_page(cur);

@@ -204,30 +237,48 @@ static void fb_deferred_io_work(struct work_struct *work) fbdefio->deferred_io(info, &fbdefio->pagelist);

/* clear the list */

• list_for_each_safe(node, next, &fbdefio->pagelist) {

• list_del_init(node);
  

• }

• list_for_each_entry_safe(pageref, next, &fbdefio->pagelist, list)

• fb_deferred_io_pageref_put(pageref, info);
  

• mutex_unlock(&fbdefio->lock);

}

-void fb_deferred_io_init(struct fb_info *info) +int fb_deferred_io_init(struct fb_info *info) { struct fb_deferred_io *fbdefio = info->fbdefio;

• struct page *page;
• unsigned int i;

• struct fb_deferred_io_pageref *pagerefs;

• unsigned long npagerefs, i;

• int ret;

  BUG_ON(!fbdefio);

• if (WARN_ON(!info->fix.smem_len))

• return -EINVAL;
  

• mutex_init(&fbdefio->lock); INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work); INIT_LIST_HEAD(&fbdefio->pagelist); if (fbdefio->delay == 0) /* set a default of 1 s */ fbdefio->delay = HZ;

• /* initialize all the page lists one time */
• for (i = 0; i < info->fix.smem_len; i += PAGE_SIZE) {

• page = fb_deferred_io_page(info, i);
  

• INIT_LIST_HEAD(&page->lru);
  

• npagerefs = DIV_ROUND_UP(info->fix.smem_len, PAGE_SIZE);
• /* alloc a page ref for each page of the display memory */
• pagerefs = kvcalloc(npagerefs, sizeof(*pagerefs), GFP_KERNEL);
• if (!pagerefs) {

• ret = -ENOMEM;
  

• goto err;
  

  }
• for (i = 0; i < npagerefs; ++i)

• INIT_LIST_HEAD(&pagerefs[i].list);
  

• info->npagerefs = npagerefs;
• info->pagerefs = pagerefs;
• return 0;

+err:

• mutex_destroy(&fbdefio->lock);
• return ret;

} EXPORT_SYMBOL_GPL(fb_deferred_io_init);

@@ -254,6 +305,7 @@ void fb_deferred_io_cleanup(struct fb_info *info) page->mapping = NULL; }

• kvfree(info->pagerefs); mutex_destroy(&fbdefio->lock);

} EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);

diff --git a/include/linux/fb.h b/include/linux/fb.h index f95da1af9ff6..a332590c0fae 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -201,6 +201,13 @@ struct fb_pixmap { };

#ifdef CONFIG_FB_DEFERRED_IO +struct fb_deferred_io_pageref {

• struct page *page;
• unsigned long offset;
• /* private */
• struct list_head list;

This is the list of pages - so this could be named pagelist...

+};

struct fb_deferred_io { /* delay between mkwrite and deferred handler */ unsigned long delay; @@ -468,6 +475,8 @@ struct fb_info { #endif #ifdef CONFIG_FB_DEFERRED_IO struct delayed_work deferred_work;

• unsigned long npagerefs;
• struct fb_deferred_io_pageref *pagerefs; struct fb_deferred_io *fbdefio;

#endif

@@ -661,7 +670,7 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,

/* drivers/video/fb_defio.c */ int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma); -extern void fb_deferred_io_init(struct fb_info *info); +extern int fb_deferred_io_init(struct fb_info *info); extern void fb_deferred_io_open(struct fb_info *info, struct inode *inode, struct file *file); -- 2.36.0

Hi Thomas,

...

...

• /* this is to find and return the vmalloc-ed fb pages */ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) {

@@ -59,7 +113,7 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) printk(KERN_ERR "no mapping available\n"); BUG_ON(!page->mapping);

• page->index = vmf->pgoff;

• page->index = vmf->pgoff; /* for page_mkclean() */ vmf->page = page; return 0;

@@ -95,7 +149,11 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) struct page *page = vmf->page; struct fb_info *info = vmf->vma->vm_private_data; struct fb_deferred_io *fbdefio = info->fbdefio;

• struct list_head *pos = &fbdefio->pagelist;

• struct fb_deferred_io_pageref *pageref;
• unsigned long offset;
• vm_fault_t ret;
• offset = (vmf->address - vmf->vma->vm_start); /* this is a callback we get when userspace first tries to write to the page. we schedule a workqueue. that workqueue

@@ -112,6 +170,12 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) if (fbdefio->first_io && list_empty(&fbdefio->pagelist)) fbdefio->first_io(info);

• pageref = fb_deferred_io_pageref_get(info, offset, page);

Compared to the old code we now do all the sorting and stuff without the page locked, which seem like a big change.

We never touch any of the page's fields in fb_deferred_io_pageref_get(). It's only used to initialize the pageref's page pointer. The pagerefs are all protected by fbdev-internal locking. Is there a reason why we should further hold the page lock?

I only commented because it was a change in scope of the lock, I did not see anything wrong in the locking, but then I do not understand locking so that does not say much.

All sorting is done by the pageref addresses, which implicitly correspond to 'offset'. After looking at the new function again, I'll change it to sort directly by offset. It's clearer in its intend.

Looks forward for the re-spin.

Sam

Hi Thomas.

On Mon, Apr 25, 2022 at 01:27:51PM +0200, Thomas Zimmermann wrote:

Refactor the page-write handler for deferred I/O. Drivers use the function to let fbdev track written pages of mmap'ed framebuffer memory.

I like how the comments got a brush up and a little more info was added. But I do not see the point of the refactoring - the code is equally readable before and after - maybe even easier before (modulus the improved comments).

But if you consider it better keep it. Again just my thoughts when reading the code.

Sam

v2:

• don't export the helper until we have an external caller

Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Javier Martinez Canillas javierm@redhat.com

---

drivers/video/fbdev/core/fb_defio.c | 68 ++++++++++++++++++++--------- 1 file changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index a03b9c64fc61..214581ce5840 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -143,29 +143,18 @@ int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy } EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);

-/* vm_ops->page_mkwrite handler */ -static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) +/*

• • Adds a page to the dirty list. Requires caller to hold
• • struct fb_deferred_io.lock. Call this from struct
• • vm_operations_struct.page_mkwrite.
• */

+static vm_fault_t __fb_deferred_io_track_page(struct fb_info *info, unsigned long offset,

• 			      struct page *page)
  

{

• struct page *page = vmf->page;

• struct fb_info *info = vmf->vma->vm_private_data; struct fb_deferred_io *fbdefio = info->fbdefio; struct fb_deferred_io_pageref *pageref;

• unsigned long offset; vm_fault_t ret;

• offset = (vmf->address - vmf->vma->vm_start);

• /* this is a callback we get when userspace first tries to

• write to the page. we schedule a workqueue. that workqueue

• will eventually mkclean the touched pages and execute the

• deferred framebuffer IO. then if userspace touches a page

• again, we repeat the same scheme */

• file_update_time(vmf->vma->vm_file);

• /* protect against the workqueue changing the page list */

• mutex_lock(&fbdefio->lock);

• /* first write in this cycle, notify the driver */ if (fbdefio->first_io && list_empty(&fbdefio->pagelist)) fbdefio->first_io(info);

@@ -186,8 +175,6 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) */ lock_page(pageref->page);

• mutex_unlock(&fbdefio->lock);
• /* come back after delay to process the deferred IO */ schedule_delayed_work(&info->deferred_work, fbdefio->delay); return VM_FAULT_LOCKED;

@@ -197,6 +184,47 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) return ret; }

+/*

• • fb_deferred_io_page_mkwrite - Mark a page as written for deferred I/O
• • @fb_info: The fbdev info structure
• • @vmf: The VM fault
• • This is a callback we get when userspace first tries to
• • write to the page. We schedule a workqueue. That workqueue
• • will eventually mkclean the touched pages and execute the
• • deferred framebuffer IO. Then if userspace touches a page
• • again, we repeat the same scheme.
• • Returns:
• • VM_FAULT_LOCKED on success, or a VM_FAULT error otherwise.
• */

+static vm_fault_t fb_deferred_io_page_mkwrite(struct fb_info *info, struct vm_fault *vmf) +{

• struct page *page = vmf->page;
• struct fb_deferred_io *fbdefio = info->fbdefio;
• unsigned long offset;
• vm_fault_t ret;
• offset = (vmf->address - vmf->vma->vm_start);
• file_update_time(vmf->vma->vm_file);
• /* protect against the workqueue changing the page list */
• mutex_lock(&fbdefio->lock);
• ret = __fb_deferred_io_track_page(info, offset, page);
• mutex_unlock(&fbdefio->lock);
• return ret;

+}

+/* vm_ops->page_mkwrite handler */ +static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) +{

• struct fb_info *info = vmf->vma->vm_private_data;
• return fb_deferred_io_page_mkwrite(info, vmf);

+}

static const struct vm_operations_struct fb_deferred_io_vm_ops = { .fault = fb_deferred_io_fault, .page_mkwrite = fb_deferred_io_mkwrite, -- 2.36.0

Hi

Am 25.04.22 um 20:24 schrieb Sam Ravnborg:

Hi Thomas.

On Mon, Apr 25, 2022 at 01:27:51PM +0200, Thomas Zimmermann wrote:

...

Refactor the page-write handler for deferred I/O. Drivers use the function to let fbdev track written pages of mmap'ed framebuffer memory.

I like how the comments got a brush up and a little more info was added. But I do not see the point of the refactoring - the code is equally readable before and after - maybe even easier before (modulus the improved comments).

FYI I'm going to move the locking into the track-page helper, which makes the code more readable.

Best regards Thomas

But if you consider it better keep it. Again just my thoughts when reading the code.

Sam

...

v2:

• don't export the helper until we have an external caller

Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Javier Martinez Canillas javierm@redhat.com

---

drivers/video/fbdev/core/fb_defio.c | 68 ++++++++++++++++++++--------- 1 file changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index a03b9c64fc61..214581ce5840 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -143,29 +143,18 @@ int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy } EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);

-/* vm_ops->page_mkwrite handler */ -static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) +/*

• • Adds a page to the dirty list. Requires caller to hold
• • struct fb_deferred_io.lock. Call this from struct
• • vm_operations_struct.page_mkwrite.
• */

+static vm_fault_t __fb_deferred_io_track_page(struct fb_info *info, unsigned long offset,

• 			      struct page *page)
  

  {

• struct page *page = vmf->page;

• struct fb_info *info = vmf->vma->vm_private_data; struct fb_deferred_io *fbdefio = info->fbdefio; struct fb_deferred_io_pageref *pageref;

• unsigned long offset; vm_fault_t ret;

• offset = (vmf->address - vmf->vma->vm_start);

• /* this is a callback we get when userspace first tries to

• write to the page. we schedule a workqueue. that workqueue

• will eventually mkclean the touched pages and execute the

• deferred framebuffer IO. then if userspace touches a page

• again, we repeat the same scheme */

• file_update_time(vmf->vma->vm_file);

• /* protect against the workqueue changing the page list */

• mutex_lock(&fbdefio->lock);

• /* first write in this cycle, notify the driver */ if (fbdefio->first_io && list_empty(&fbdefio->pagelist)) fbdefio->first_io(info);

@@ -186,8 +175,6 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) */ lock_page(pageref->page);

• mutex_unlock(&fbdefio->lock);
• /* come back after delay to process the deferred IO */ schedule_delayed_work(&info->deferred_work, fbdefio->delay); return VM_FAULT_LOCKED;

@@ -197,6 +184,47 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) return ret; }

+/*

• • fb_deferred_io_page_mkwrite - Mark a page as written for deferred I/O
• • @fb_info: The fbdev info structure
• • @vmf: The VM fault
• • This is a callback we get when userspace first tries to
• • write to the page. We schedule a workqueue. That workqueue
• • will eventually mkclean the touched pages and execute the
• • deferred framebuffer IO. Then if userspace touches a page
• • again, we repeat the same scheme.
• • Returns:
• • VM_FAULT_LOCKED on success, or a VM_FAULT error otherwise.
• */

+static vm_fault_t fb_deferred_io_page_mkwrite(struct fb_info *info, struct vm_fault *vmf) +{

• struct page *page = vmf->page;
• struct fb_deferred_io *fbdefio = info->fbdefio;
• unsigned long offset;
• vm_fault_t ret;
• offset = (vmf->address - vmf->vma->vm_start);
• file_update_time(vmf->vma->vm_file);
• /* protect against the workqueue changing the page list */
• mutex_lock(&fbdefio->lock);
• ret = __fb_deferred_io_track_page(info, offset, page);
• mutex_unlock(&fbdefio->lock);
• return ret;

+}

+/* vm_ops->page_mkwrite handler */ +static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) +{

• struct fb_info *info = vmf->vma->vm_private_data;
• return fb_deferred_io_page_mkwrite(info, vmf);

+}

• static const struct vm_operations_struct fb_deferred_io_vm_ops = { .fault = fb_deferred_io_fault, .page_mkwrite = fb_deferred_io_mkwrite,

-- 2.36.0