The patch titled
Subject: mm/madvise: MADV_COLLAPSE return EAGAIN when page cannot be isolated
has been added to the -mm mm-unstable branch. Its filename is
mm-madvise-madv_collapse-return-eagain-when-page-cannot-be-isolated.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-madvise-madv_collapse-return-eagain-when-page-cannot-be-isolated.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Zach O'Keefe" <zokeefe@xxxxxxxxxx>
Subject: mm/madvise: MADV_COLLAPSE return EAGAIN when page cannot be isolated
Date: Thu, 22 Sep 2022 11:46:50 -0700
MADV_COLLAPSE is a best-effort request that attempts to set an actionable
errno value if the request cannot be fulfilled at the time. EAGAIN should
be used to communicate that a resource was temporarily unavailable, but
that the user may try again immediately.
SCAN_DEL_PAGE_LRU is an internal result code used when a page cannot be
isolated from it's LRU list. Since this, like SCAN_PAGE_LRU, is likely a
transitory state, make MADV_COLLAPSE return EAGAIN so that users know they
may reattempt the operation.
Another important scenario to consider is race with khugepaged.
khugepaged might isolate a page while MADV_COLLAPSE is interested in it.
Even though racing with khugepaged might mean that the memory has already
been collapsed, signalling an errno that is non-intrinsic to that memory
or arguments provided to madvise(2) lets the user know that future
attempts might (and in this case likely would) succeed, and avoids
false-negative assumptions by the user.
Link: https://lkml.kernel.org/r/20220922184651.1016461-1-zokeefe@xxxxxxxxxx
Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse")
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Chris Kennelly <ckennelly@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/khugepaged.c~mm-madvise-madv_collapse-return-eagain-when-page-cannot-be-isolated
+++ a/mm/khugepaged.c
@@ -2372,6 +2372,7 @@ static int madvise_collapse_errno(enum s
/* Resource temporary unavailable - trying again might succeed */
case SCAN_PAGE_LOCK:
case SCAN_PAGE_LRU:
+ case SCAN_DEL_PAGE_LRU:
return -EAGAIN;
/*
* Other: Trying again likely not to succeed / error intrinsic to
@@ -2454,6 +2455,7 @@ int madvise_collapse(struct vm_area_stru
case SCAN_PAGE_LOCK:
case SCAN_PAGE_COMPOUND:
case SCAN_PAGE_LRU:
+ case SCAN_DEL_PAGE_LRU:
last_fail = result;
break;
default:
_
Patches currently in -mm which might be from zokeefe@xxxxxxxxxx are
mm-khugepaged-check-compound_order-in-collapse_pte_mapped_thp.patch
mm-madvise-madv_collapse-return-eagain-when-page-cannot-be-isolated.patch
selftests-vm-retry-on-eagain-for-madv_collapse-selftest.patch
mm-shmem-add-flag-to-enforce-shmem-thp-in-hugepage_vma_check.patch
mm-khugepaged-attempt-to-map-file-shmem-backed-pte-mapped-thps-by-pmds.patch
mm-madvise-add-file-and-shmem-support-to-madv_collapse.patch
mm-khugepaged-add-tracepoint-to-hpage_collapse_scan_file.patch
selftests-vm-dedup-thp-helpers.patch
selftests-vm-modularize-thp-collapse-memory-operations.patch
selftests-vm-add-thp-collapse-file-and-tmpfs-testing.patch
selftests-vm-add-thp-collapse-shmem-testing.patch
selftests-vm-add-file-shmem-madv_collapse-selftest-for-cleared-pmd.patch
selftests-vm-add-selftest-for-madv_collapse-of-uffd-minor-memory.patch
