On Wednesday, 3 March 2021 9:08:15 AM AEDT Zi Yan wrote:
On 26 Feb 2021, at 2:18, Alistair Popple wrote:
diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 7f1ee411bd7b..77fa17de51d7 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -86,8 +86,6 @@ struct anon_vma_chain { };
enum ttu_flags {
- TTU_MIGRATION = 0x1, /* migration mode */
- TTU_SPLIT_HUGE_PMD = 0x4, /* split huge PMD if any */
It implies freeze in try_to_migrate() and no freeze in try_to_unmap(). I
think
we need some comments here, above try_to_migrate(), and above try_to_unmap() to clarify the implication.
Sure. This confused me for a bit and I was initially tempted to leave TTU_SPLIT_FREEZE as a separate mode flag but looking at what freeze actually does it made sense to remove it because try_to_migrate() is for installing migration entries (which is what freeze does) and try_to_unmap() just unmaps. So I'll add some comments to that effect.
TTU_IGNORE_MLOCK = 0x8, /* ignore mlock */ TTU_IGNORE_HWPOISON = 0x20, /* corrupted page is recoverable */ @@ -96,7 +94,6 @@ enum ttu_flags { * do a final flush if necessary */ TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock: * caller holds it */
- TTU_SPLIT_FREEZE = 0x100, /* freeze pte under splitting thp */
};
#ifdef CONFIG_MMU @@ -193,6 +190,7 @@ static inline void page_dup_rmap(struct page *page,
bool compound)
int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg, unsigned long *vm_flags);
+bool try_to_migrate(struct page *page, enum ttu_flags flags); bool try_to_unmap(struct page *, enum ttu_flags flags);
/* Avoid racy checks */ diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d00b93dc2d9e..357052a4567b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2351,16 +2351,16 @@ void vma_adjust_trans_huge(struct vm_area_struct
*vma,
static void unmap_page(struct page *page) {
- enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK |
TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD; bool unmap_success;
VM_BUG_ON_PAGE(!PageHead(page), page);
if (PageAnon(page))
ttu_flags |= TTU_SPLIT_FREEZE;- unmap_success = try_to_unmap(page, ttu_flags);
unmap_success = try_to_migrate(page, ttu_flags);- else
unmap_success = try_to_unmap(page, ttu_flags |TTU_IGNORE_MLOCK);I think we need a comment here about why anonymous pages need
try_to_migrate()
and others need try_to_unmap().
Historically this comes from baa355fd3314 ("thp: file pages support for split_huge_page()") which says:
"We don't setup migration entries. Just unmap pages. It helps handling cases when i_size is in the middle of the page: no need handle unmap pages beyond i_size manually."
But I'll add a comment here, thanks.
- Alistair
Thanks.
— Best Regards, Yan Zi