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 <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Song Liu <[email protected]>
---
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
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 <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Hugh Dickins <[email protected]>
> Cc: William Kucharski <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Signed-off-by: Song Liu <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
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 <[email protected]>
> > Cc: Johannes Weiner <[email protected]>
> > Cc: Hugh Dickins <[email protected]>
> > Cc: William Kucharski <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Signed-off-by: Song Liu <[email protected]>
>
> Acked-by: Johannes Weiner <[email protected]>
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);
> On Oct 18, 2019, at 9:58 AM, Johannes Weiner <[email protected]> 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 <[email protected]>
>>> Cc: Johannes Weiner <[email protected]>
>>> Cc: Hugh Dickins <[email protected]>
>>> Cc: William Kucharski <[email protected]>
>>> Cc: Andrew Morton <[email protected]>
>>> Signed-off-by: Song Liu <[email protected]>
>>
>> Acked-by: Johannes Weiner <[email protected]>
>
> 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);