The patch titled Subject: mm/MADV_COLLAPSE: set EAGAIN on unexpected page refcount has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-madv_collapse-set-eagain-on-unexpected-page-refcount.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Zach O'Keefe" zokeefe@google.com Subject: mm/MADV_COLLAPSE: set EAGAIN on unexpected page refcount Date: Tue, 24 Jan 2023 17:57:37 -0800

During collapse, in a few places we check to see if a given small page has any unaccounted references. If the refcount on the page doesn't match our expectations, it must be there is an unknown user concurrently interested in the page, and so it's not safe to move the contents elsewhere. However, the unaccounted pins are likely an ephemeral state.

In such a situation, make MADV_COLLAPSE set EAGAIN errno, indicating that collapse may succeed on retry.

Link: https://lkml.kernel.org/r/20230125015738.912924-1-zokeefe@google.com Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") Signed-off-by: Zach O'Keefe zokeefe@google.com Reported-by: Hugh Dickins hughd@google.com Acked-by: Hugh Dickins hughd@google.com Reviewed-by: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 1 + 1 file changed, 1 insertion(+)

--- a/mm/khugepaged.c~mm-madv_collapse-set-eagain-on-unexpected-page-refcount +++ a/mm/khugepaged.c @@ -2611,6 +2611,7 @@ static int madvise_collapse_errno(enum s case SCAN_CGROUP_CHARGE_FAIL: return -EBUSY; /* Resource temporary unavailable - trying again might succeed */ + case SCAN_PAGE_COUNT: case SCAN_PAGE_LOCK: case SCAN_PAGE_LRU: case SCAN_DEL_PAGE_LRU: _

Patches currently in -mm which might be from zokeefe@google.com are

mm-madv_collapse-set-eagain-on-unexpected-page-refcount.patch