Re: [PATCH 1/3] drm/ttm: rework ttm_tt page limit v3

On Thu, Jan 28, 2021 at 02:16:02PM +0100, Christian König wrote:

TTM implements a rather extensive accounting of allocated memory.

There are two reasons for this:

1. It tries to block userspace allocating a huge number of very small BOs without accounting for the kmalloced memory.

2. Make sure we don't over allocate and run into an OOM situation during swapout while trying to handle the memory shortage.

This is only partially a good idea. First of all it is perfectly valid for an application to use all of system memory, limiting it to 50% is not really acceptable.

What we need to take care of is that the application is held accountable for the memory it allocated. This is what control mechanisms like memcg and the normal Linux page accounting already do.

Making sure that we don't run into an OOM situation while trying to cope with a memory shortage is still a good idea, but this is also not very well implemented since it means another opportunity of recursion from the driver back into TTM.

So start to rework all of this by implementing a shrinker callback which allows for TT object to be swapped out if necessary.

v2: Switch from limit to shrinker callback. v3: fix gfp mask handling, use atomic for swapable_pages, add debugfs

Signed-off-by: Christian König christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_bo.c | 4 +- drivers/gpu/drm/ttm/ttm_memory.c | 7 +- drivers/gpu/drm/ttm/ttm_tt.c | 111 ++++++++++++++++++++++++++-- drivers/gpu/drm/vmwgfx/vmwgfx_drv.c | 2 +- include/drm/ttm/ttm_bo_api.h | 2 +- include/drm/ttm/ttm_tt.h | 6 +- 6 files changed, 117 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index 20256797f3a6..643befc1a6f2 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -1219,7 +1219,7 @@ EXPORT_SYMBOL(ttm_bo_wait);

• A buffer object shrink method that tries to swap out the first
• buffer object on the bo_global::swap_lru list.

*/ -int ttm_bo_swapout(struct ttm_operation_ctx *ctx) +int ttm_bo_swapout(struct ttm_operation_ctx *ctx, gfp_t gfp_flags) { struct ttm_global *glob = &ttm_glob; struct ttm_buffer_object *bo; @@ -1302,7 +1302,7 @@ int ttm_bo_swapout(struct ttm_operation_ctx *ctx) if (bo->bdev->funcs->swap_notify) bo->bdev->funcs->swap_notify(bo);

• ret = ttm_tt_swapout(bo->bdev, bo->ttm);

• ret = ttm_tt_swapout(bo->bdev, bo->ttm, gfp_flags);

out:

/** diff --git a/drivers/gpu/drm/ttm/ttm_memory.c b/drivers/gpu/drm/ttm/ttm_memory.c index a3bfbd9cea68..634a85c2dc4c 100644 --- a/drivers/gpu/drm/ttm/ttm_memory.c +++ b/drivers/gpu/drm/ttm/ttm_memory.c @@ -37,6 +37,7 @@ #include <linux/slab.h> #include <linux/swap.h> #include <drm/ttm/ttm_pool.h> +#include <drm/ttm/ttm_tt.h>

#include "ttm_module.h"

@@ -276,9 +277,9 @@ static void ttm_shrink(struct ttm_mem_global *glob, bool from_wq,

while (ttm_zones_above_swap_target(glob, from_wq, extra)) { spin_unlock(&glob->lock);

• ret = ttm_bo_swapout(ctx);
  

• ret = ttm_bo_swapout(ctx, GFP_KERNEL);
  

  spin_lock(&glob->lock);

• if (unlikely(ret != 0))
  

• if (unlikely(ret < 0))
  break;
  

  }

@@ -453,6 +454,7 @@ int ttm_mem_global_init(struct ttm_mem_global *glob) zone->name, (unsigned long long)zone->max_mem >> 10); } ttm_pool_mgr_init(glob->zone_kernel->max_mem/(2*PAGE_SIZE));

• ttm_tt_mgr_init(); return 0;

out_no_zone: ttm_mem_global_release(glob); @@ -466,6 +468,7 @@ void ttm_mem_global_release(struct ttm_mem_global *glob)

/* let the page allocator first stop the shrink work. */ ttm_pool_mgr_fini();

• ttm_tt_mgr_fini();

  flush_workqueue(glob->swap_queue); destroy_workqueue(glob->swap_queue);

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c index 7782d5393c7c..b67795de228d 100644 --- a/drivers/gpu/drm/ttm/ttm_tt.c +++ b/drivers/gpu/drm/ttm/ttm_tt.c @@ -38,6 +38,11 @@ #include <drm/drm_cache.h> #include <drm/ttm/ttm_bo_driver.h>

+#include "ttm_module.h"

+static struct shrinker mm_shrinker; +static atomic_long_t swapable_pages;

/*

• Allocates a ttm structure for the given BO.

*/ @@ -223,32 +228,41 @@ int ttm_tt_swapin(struct ttm_tt *ttm) return ret; }

-int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm) +/**

• • ttm_tt_swapout - swap out tt object
• • @bdev: TTM device structure.
• • @ttm: The struct ttm_tt.
• • @gfp_flags: Flags to use for memory allocation.
• • Swapout a TT object to a shmem_file, return number of pages swapped out or
• • negative error code.
• */

+int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm,

•    gfp_t gfp_flags)
  

{

• loff_t size = (loff_t)ttm->num_pages << PAGE_SHIFT; struct address_space *swap_space; struct file *swap_storage; struct page *from_page; struct page *to_page;

• gfp_t gfp_mask; int i, ret;

• swap_storage = shmem_file_setup("ttm swap",

• 			ttm->num_pages << PAGE_SHIFT,
  

• 			0);
  

• swap_storage = shmem_file_setup("ttm swap", size, 0); if (IS_ERR(swap_storage)) { pr_err("Failed allocating swap storage\n"); return PTR_ERR(swap_storage); }

  swap_space = swap_storage->f_mapping;

• gfp_mask = mapping_gfp_mask(swap_space);

• gfp_flags &= mapping_gfp_mask(swap_space);

  for (i = 0; i < ttm->num_pages; ++i) { from_page = ttm->pages[i]; if (unlikely(from_page == NULL)) continue;

• to_page = shmem_read_mapping_page_gfp(swap_space, i, gfp_mask);
  

• to_page = shmem_read_mapping_page_gfp(swap_space, i, gfp_flags);
  

  if (IS_ERR(to_page)) { ret = PTR_ERR(to_page); goto out_err;

@@ -263,7 +277,7 @@ int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm) ttm->swap_storage = swap_storage; ttm->page_flags |= TTM_PAGE_FLAG_SWAPPED;

• return 0;

• return ttm->num_pages;

out_err: fput(swap_storage); @@ -280,6 +294,8 @@ static void ttm_tt_add_mapping(struct ttm_device *bdev, struct ttm_tt *ttm)

for (i = 0; i < ttm->num_pages; ++i) ttm->pages[i]->mapping = bdev->dev_mapping;

• atomic_long_add(ttm->num_pages, &swapable_pages);

}

int ttm_tt_populate(struct ttm_device *bdev, @@ -326,6 +342,8 @@ static void ttm_tt_clear_mapping(struct ttm_tt *ttm) (*page)->mapping = NULL; (*page++)->index = 0; }

• atomic_long_sub(ttm->num_pages, &swapable_pages);

}

void ttm_tt_unpopulate(struct ttm_device *bdev, @@ -341,3 +359,80 @@ void ttm_tt_unpopulate(struct ttm_device *bdev, ttm_pool_free(&bdev->pool, ttm); ttm->page_flags &= ~TTM_PAGE_FLAG_PRIV_POPULATED; }

+/* As long as pages are available make sure to release at least one */ +static unsigned long ttm_tt_shrinker_scan(struct shrinker *shrink,

• 			  struct shrink_control *sc)
  

+{

• struct ttm_operation_ctx ctx = {

• .no_wait_gpu = false
  

• };
• int ret;
• if (!(sc->gfp_mask & __GFP_FS))

• return SHRINK_EMPTY;
  

These two checks here still look like cargo cult to me. I thought the gfp_mask you're getting is for numa/zone-aware shrinking, which we're not doing. __GFP_FS in the shrinker is a bug.

Maybe convert to WARN_ON to convince yourself, test, then remove? If you ever get __GFP_FS context in a shrinker lockdep will start screaming real fast :-)

With that addressed:

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

• ret = ttm_bo_swapout(&ctx, GFP_NOFS);
• return ret < 0 ? SHRINK_EMPTY : ret;

+}

+/* Return the number of pages available or SHRINK_EMPTY if we have none */ +static unsigned long ttm_tt_shrinker_count(struct shrinker *shrink,

• 			   struct shrink_control *sc)
  

+{

• unsigned long num_pages;
• if (!(sc->gfp_mask & __GFP_FS))

• return SHRINK_EMPTY;
  

• num_pages = atomic_long_read(&swapable_pages);
• return num_pages ? num_pages : SHRINK_EMPTY;

+}

+#ifdef CONFIG_DEBUG_FS

+/* Test the shrinker functions and dump the result */ +static int ttm_tt_debugfs_shrink_show(struct seq_file *m, void *data) +{

• struct shrink_control sc = { .gfp_mask = GFP_KERNEL };
• fs_reclaim_acquire(GFP_KERNEL);
• seq_printf(m, "%lu/%lu\n", ttm_tt_shrinker_count(&mm_shrinker, &sc),

•    ttm_tt_shrinker_scan(&mm_shrinker, &sc));
  

• fs_reclaim_release(GFP_KERNEL);
• return 0;

+} +DEFINE_SHOW_ATTRIBUTE(ttm_tt_debugfs_shrink);

+#endif

+/**

• • ttm_tt_mgr_init - register with the MM shrinker
• • Register with the MM shrinker for swapping out BOs.
• */

+int ttm_tt_mgr_init(void) +{ +#ifdef CONFIG_DEBUG_FS

• debugfs_create_file("tt_shrink", 0400, ttm_debugfs_root, NULL,

• 	    &ttm_tt_debugfs_shrink_fops);
  

+#endif

• mm_shrinker.count_objects = ttm_tt_shrinker_count;
• mm_shrinker.scan_objects = ttm_tt_shrinker_scan;
• mm_shrinker.seeks = 1;
• return register_shrinker(&mm_shrinker);

+}

+/**

• • ttm_tt_mgr_fini - unregister our MM shrinker
• • Unregisters the MM shrinker.
• */

+void ttm_tt_mgr_fini(void) +{

• unregister_shrinker(&mm_shrinker);

+} diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c index b454d80c273e..710ba5169a74 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c @@ -1383,7 +1383,7 @@ static int vmw_pm_freeze(struct device *kdev) vmw_execbuf_release_pinned_bo(dev_priv); vmw_resource_evict_all(dev_priv); vmw_release_device_early(dev_priv);

• while (ttm_bo_swapout(&ctx) == 0);

• while (ttm_bo_swapout(&ctx, GFP_KERNEL) > 0); if (dev_priv->enable_fb) vmw_fifo_resource_dec(dev_priv); if (atomic_read(&dev_priv->num_fifo_resources) != 0) {

diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h index 62734db0b421..1297a8fb7ccb 100644 --- a/include/drm/ttm/ttm_bo_api.h +++ b/include/drm/ttm/ttm_bo_api.h @@ -569,7 +569,7 @@ ssize_t ttm_bo_io(struct ttm_device *bdev, struct file *filp, const char __user *wbuf, char __user *rbuf, size_t count, loff_t *f_pos, bool write);

-int ttm_bo_swapout(struct ttm_operation_ctx *ctx); +int ttm_bo_swapout(struct ttm_operation_ctx *ctx, gfp_t gfp_flags);

/**

• ttm_bo_uses_embedded_gem_object - check if the given bo uses the

diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h index 0020a0588985..cce57fb49e2c 100644 --- a/include/drm/ttm/ttm_tt.h +++ b/include/drm/ttm/ttm_tt.h @@ -135,7 +135,8 @@ void ttm_tt_destroy_common(struct ttm_device *bdev, struct ttm_tt *ttm);

• Swap in a previously swap out ttm_tt.

*/ int ttm_tt_swapin(struct ttm_tt *ttm); -int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm); +int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm,

•    gfp_t gfp_flags);
  
  

/**

• ttm_tt_populate - allocate pages for a ttm

@@ -155,6 +156,9 @@ int ttm_tt_populate(struct ttm_device *bdev, struct ttm_tt *ttm, struct ttm_oper */ void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm);

+int ttm_tt_mgr_init(void); +void ttm_tt_mgr_fini(void);

#if IS_ENABLED(CONFIG_AGP) #include <linux/agp_backend.h>

-- 2.25.1