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mm/collapse: call collapse_file() from collapse_single_pmd()

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collapse_scan_file() reads the page cache to decide whether a table is
worth collapsing and, when it is, calls collapse_file() itself.  The
caller cannot get between the decision and the collapse.

Move the collapse_file() call up into collapse_single_pmd(), so the scan
stops at the decision.

Two things change with it.  The writeback retry re-runs collapse_file()
alone instead of rescanning first; collapse_file() repeats the scan's
checks under the page cache lock anyway.  And mm_khugepaged_scan_file
fires before the collapse, so for an accepted table its status reads
SCAN_SUCCEED; what the collapse made of the table is for
mm_khugepaged_collapse_file to report.

Preparation for splitting a collapse into a scan under mmap_lock and a
run without it.  The file scan has to stop where the anonymous one will.

Link: https://lore.kernel.org/20261014171145.3292736-9-kas@kernel.org
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Assisted-by: LLM
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
This commit is contained in:
Kiryl Shutsemau (Meta) 2026-10-14 18:11:41 +01:00 committed by Andrew Morton
parent e7c4148ad1
commit a2d1c9ea76
1 changed files with 13 additions and 8 deletions
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21
mm/khugepaged.c
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@ -2763,13 +2763,9 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm,
else
cc->progress += HPAGE_PMD_NR;
if (result == SCAN_SUCCEED) {
if (present < HPAGE_PMD_NR - max_ptes_none) {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
} else {
result = collapse_file(mm, addr, file, start, cc);
}
if (result == SCAN_SUCCEED && present < HPAGE_PMD_NR - max_ptes_none) {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
}
trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, swap, result);
@ -2800,8 +2796,16 @@ static enum scan_result collapse_single_pmd(unsigned long addr,
mmap_read_unlock(mm);
*lock_dropped = true;
retry:
/*
* SCAN_PTE_MAPPED_HUGEPAGE is work too: the page cache already holds
* the PMD folio, and only the PTE table is left to retract.
*/
result = collapse_scan_file(mm, addr, file, pgoff, cc);
if (result != SCAN_SUCCEED)
goto put;
retry:
result = collapse_file(mm, addr, file, pgoff, cc);
/* Dirty pages are worth a writeback and one more try, if asked for */
if (cc->policy.file_writeback_dirty && result == SCAN_PAGE_DIRTY_OR_WRITEBACK &&
@ -2813,6 +2817,7 @@ static enum scan_result collapse_single_pmd(unsigned long addr,
triggered_wb = true;
goto retry;
}
put:
fput(file);
if (result == SCAN_PTE_MAPPED_HUGEPAGE) {