All of lore.kernel.org
 help / color / mirror / Atom feed
* [PATCH v2] mm,thp: recheck each page before collapsing file THP
@ 2019-10-18 16:37 Song Liu
  2019-10-18 16:49 ` Johannes Weiner
  0 siblings, 1 reply; 4+ messages in thread
From: Song Liu @ 2019-10-18 16:37 UTC (permalink / raw)
  To: linux-kernel, linux-mm, akpm
  Cc: matthew.wilcox, kernel-team, william.kucharski, kirill.shutemov,
	Song Liu, Johannes Weiner, Hugh Dickins

In collapse_file(), after locking the page, it is necessary to recheck
that the page is up-to-date. Add PageUptodate() check for both shmem THP
and file THP.

Current khugepaged should not try to collapse dirty file THP, because it
is limited to read only text. Add a PageDirty check and warning for file
THP. This is added after page_mapping() check, because if the page is
truncated, it might be dirty.

Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Song Liu <songliubraving@fb.com>

---
Changes v1 => v2:
Rearrange the checks per feedback from Johannes, Rik, and Kirill. 

---
 mm/khugepaged.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0a1b4b484ac5..40c549302d36 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1626,7 +1626,12 @@ static void collapse_file(struct mm_struct *mm,
 		 * without racing with truncate.
 		 */
 		VM_BUG_ON_PAGE(!PageLocked(page), page);
-		VM_BUG_ON_PAGE(!PageUptodate(page), page);
+
+		/* double check the page is up to date */
+		if (unlikely(!PageUptodate(page))) {
+			result = SCAN_FAIL;
+			goto out_unlock;
+		}
 
 		/*
 		 * If file was truncated then extended, or hole-punched, before
@@ -1642,6 +1647,15 @@ static void collapse_file(struct mm_struct *mm,
 			goto out_unlock;
 		}
 
+		/*
+		 * khugepaged should not try to collapse dirty pages for
+		 * file THP. Show warning if this somehow happens.
+		 */
+		if (WARN_ON_ONCE(!is_shmem && PageDirty(page))) {
+			result = SCAN_FAIL;
+			goto out_unlock;
+		}
+
 		if (isolate_lru_page(page)) {
 			result = SCAN_DEL_PAGE_LRU;
 			goto out_unlock;
-- 
2.17.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread
* Re: [PATCH v2] mm,thp: recheck each page before collapsing file THP
  2019-10-18 16:37 [PATCH v2] mm,thp: recheck each page before collapsing file THP Song Liu
@ 2019-10-18 16:49 ` Johannes Weiner
  2019-10-18 16:58   ` Johannes Weiner
  0 siblings, 1 reply; 4+ messages in thread
From: Johannes Weiner @ 2019-10-18 16:49 UTC (permalink / raw)
  To: Song Liu
  Cc: linux-kernel, linux-mm, akpm, matthew.wilcox, kernel-team,
	william.kucharski, kirill.shutemov, Hugh Dickins

On Fri, Oct 18, 2019 at 09:37:54AM -0700, Song Liu wrote:
> In collapse_file(), after locking the page, it is necessary to recheck
> that the page is up-to-date. Add PageUptodate() check for both shmem THP
> and file THP.
> 
> Current khugepaged should not try to collapse dirty file THP, because it
> is limited to read only text. Add a PageDirty check and warning for file
> THP. This is added after page_mapping() check, because if the page is
> truncated, it might be dirty.
> 
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: William Kucharski <william.kucharski@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Song Liu <songliubraving@fb.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

^ permalink raw reply	[flat|nested] 4+ messages in thread
* Re: [PATCH v2] mm,thp: recheck each page before collapsing file THP
  2019-10-18 16:49 ` Johannes Weiner
@ 2019-10-18 16:58   ` Johannes Weiner
  2019-10-18 17:27     ` Song Liu
  0 siblings, 1 reply; 4+ messages in thread
From: Johannes Weiner @ 2019-10-18 16:58 UTC (permalink / raw)
  To: Song Liu
  Cc: linux-kernel, linux-mm, akpm, matthew.wilcox, kernel-team,
	william.kucharski, kirill.shutemov, Hugh Dickins

On Fri, Oct 18, 2019 at 12:49:46PM -0400, Johannes Weiner wrote:
> On Fri, Oct 18, 2019 at 09:37:54AM -0700, Song Liu wrote:
> > In collapse_file(), after locking the page, it is necessary to recheck
> > that the page is up-to-date. Add PageUptodate() check for both shmem THP
> > and file THP.
> > 
> > Current khugepaged should not try to collapse dirty file THP, because it
> > is limited to read only text. Add a PageDirty check and warning for file
> > THP. This is added after page_mapping() check, because if the page is
> > truncated, it might be dirty.
> > 
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Hugh Dickins <hughd@google.com>
> > Cc: William Kucharski <william.kucharski@oracle.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Song Liu <songliubraving@fb.com>
> 
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

We should also be able to remove the unlocked tests for those two
conditions, right?

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0a1b4b484ac5..a3ef6ce86bfa 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1601,17 +1601,6 @@ static void collapse_file(struct mm_struct *mm,
 					result = SCAN_FAIL;
 					goto xa_unlocked;
 				}
-			} else if (!PageUptodate(page)) {
-				xas_unlock_irq(&xas);
-				wait_on_page_locked(page);
-				if (!trylock_page(page)) {
-					result = SCAN_PAGE_LOCK;
-					goto xa_unlocked;
-				}
-				get_page(page);
-			} else if (PageDirty(page)) {
-				result = SCAN_FAIL;
-				goto xa_locked;
 			} else if (trylock_page(page)) {
 				get_page(page);
 				xas_unlock_irq(&xas);

^ permalink raw reply related	[flat|nested] 4+ messages in thread
* Re: [PATCH v2] mm,thp: recheck each page before collapsing file THP
  2019-10-18 16:58   ` Johannes Weiner
@ 2019-10-18 17:27     ` Song Liu
  0 siblings, 0 replies; 4+ messages in thread
From: Song Liu @ 2019-10-18 17:27 UTC (permalink / raw)
  To: Johannes Weiner
  Cc: open list, linux-mm, akpm, matthew.wilcox, Kernel Team,
	william.kucharski, kirill.shutemov, Hugh Dickins



> On Oct 18, 2019, at 9:58 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
> On Fri, Oct 18, 2019 at 12:49:46PM -0400, Johannes Weiner wrote:
>> On Fri, Oct 18, 2019 at 09:37:54AM -0700, Song Liu wrote:
>>> In collapse_file(), after locking the page, it is necessary to recheck
>>> that the page is up-to-date. Add PageUptodate() check for both shmem THP
>>> and file THP.
>>> 
>>> Current khugepaged should not try to collapse dirty file THP, because it
>>> is limited to read only text. Add a PageDirty check and warning for file
>>> THP. This is added after page_mapping() check, because if the page is
>>> truncated, it might be dirty.
>>> 
>>> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
>>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>> Cc: Hugh Dickins <hughd@google.com>
>>> Cc: William Kucharski <william.kucharski@oracle.com>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> 
>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> We should also be able to remove the unlocked tests for those two
> conditions, right?

Yeah, I think we can remove them. 

Thanks,
Song

> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 0a1b4b484ac5..a3ef6ce86bfa 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1601,17 +1601,6 @@ static void collapse_file(struct mm_struct *mm,
> 					result = SCAN_FAIL;
> 					goto xa_unlocked;
> 				}
> -			} else if (!PageUptodate(page)) {
> -				xas_unlock_irq(&xas);
> -				wait_on_page_locked(page);
> -				if (!trylock_page(page)) {
> -					result = SCAN_PAGE_LOCK;
> -					goto xa_unlocked;
> -				}
> -				get_page(page);
> -			} else if (PageDirty(page)) {
> -				result = SCAN_FAIL;
> -				goto xa_locked;
> 			} else if (trylock_page(page)) {
> 				get_page(page);
> 				xas_unlock_irq(&xas);


^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-10-18 17:27 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-18 16:37 [PATCH v2] mm,thp: recheck each page before collapsing file THP Song Liu
2019-10-18 16:49 ` Johannes Weiner
2019-10-18 16:58   ` Johannes Weiner
2019-10-18 17:27     ` Song Liu

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.