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authorZach O'Keefe <zokeefe@google.com>2022-09-22 11:46:50 -0700
committerAndrew Morton <akpm@linux-foundation.org>2022-10-03 14:03:32 -0700
commit0f3e2a2c4243695c5ac3fbccce18dc74c0250df6 (patch)
tree61961b0f96bfabe09b09d670ed74ad72b55b89f6 /mm/khugepaged.c
parent780a4b6fb865534fcb3aa9150942f3a719d11ce9 (diff)
mm/madvise: MADV_COLLAPSE return EAGAIN when page cannot be isolated
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@google.com Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") Signed-off-by: Zach O'Keefe <zokeefe@google.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Chris Kennelly <ckennelly@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: James Houghton <jthoughton@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com> Cc: SeongJae Park <sj@kernel.org> Cc: Song Liu <songliubraving@fb.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 40fd9f7b3ed3..b3ebe90a66d9 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2372,6 +2372,7 @@ static int madvise_collapse_errno(enum scan_result r)
/* 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_struct *vma, struct vm_area_struct **prev,
case SCAN_PAGE_LOCK:
case SCAN_PAGE_COMPOUND:
case SCAN_PAGE_LRU:
+ case SCAN_DEL_PAGE_LRU:
last_fail = result;
break;
default: