The patch titled
Subject: mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)
has been added to the -mm tree. Its filename is
mm-thp-collapse_file-do-try_to_unmapttu_batch_flush.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-collapse_file-do-try_to_unmapttu_batch_flush.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-collapse_file-do-try_to_unmapttu_batch_flush.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)
collapse_file() is using unmap_mapping_pages(1) on each small page found
mapped, unlike others (reclaim, migration, splitting, memory-failure) who
use try_to_unmap(). There are four advantages to try_to_unmap(): first,
its TTU_IGNORE_MLOCK option now avoids leaving mlocked page in pagevec;
second, its vma lookup uses i_mmap_lock_read() not i_mmap_lock_write();
third, it breaks out early if page is not mapped everywhere it might be;
fourth, its TTU_BATCH_FLUSH option can be used, as in page reclaim, to
save up all the TLB flushing until all of the pages have been unmapped.
Wild guess: perhaps it was originally written to use try_to_unmap(), but
hit the VM_BUG_ON_PAGE(page_mapped) after unmapping, because without
TTU_SYNC it may skip page table locks; but unmap_mapping_pages() never
skips them, so fixed the issue. I did once hit that VM_BUG_ON_PAGE()
since making this change: we could pass TTU_SYNC here, but I think just
delete the check - the race is very rare, this is an ordinary small page
so we don't need to be so paranoid about mapcount surprises, and the
page_ref_freeze() just below already handles the case adequately.
Link: https://lkml.kernel.org/r/c390e7b-7648-b3e9-9ae1-87c9b9e95ed4@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/khugepaged.c~mm-thp-collapse_file-do-try_to_unmapttu_batch_flush
+++ a/mm/khugepaged.c
@@ -1823,13 +1823,12 @@ static void collapse_file(struct mm_stru
}
if (page_mapped(page))
- unmap_mapping_pages(mapping, index, 1, false);
+ try_to_unmap(page, TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
xas_lock_irq(&xas);
xas_set(&xas, index);
VM_BUG_ON_PAGE(page != xas_load(&xas), page);
- VM_BUG_ON_PAGE(page_mapped(page), page);
/*
* The page is expected to have page_count() == 3:
@@ -1893,6 +1892,13 @@ xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
+ /*
+ * If collapse is successful, flush must be done now before copying.
+ * If collapse is unsuccessful, does flush actually need to be done?
+ * Do it anyway, to clear the state.
+ */
+ try_to_unmap_flush();
+
if (result == SCAN_SUCCEED) {
struct page *page, *tmp;
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-munlock-delete-page_mlock-and-all-its-works.patch
mm-munlock-delete-foll_mlock-and-foll_populate.patch
mm-munlock-delete-munlock_vma_pages_all-allow-oomreap.patch
mm-munlock-rmap-call-mlock_vma_page-munlock_vma_page.patch
mm-munlock-replace-clear_page_mlock-by-final-clearance.patch
mm-munlock-maintain-page-mlock_count-while-unevictable.patch
mm-munlock-mlock_pte_range-when-mlocking-or-munlocking.patch
mm-migrate-__unmap_and_move-push-good-newpage-to-lru.patch
mm-munlock-delete-smp_mb-from-__pagevec_lru_add_fn.patch
mm-munlock-mlock_page-munlock_page-batch-by-pagevec.patch
mm-munlock-page-migration-needs-mlock-pagevec-drained.patch
mm-thp-collapse_file-do-try_to_unmapttu_batch_flush.patch
mm-thp-shrink_page_list-avoid-splitting-vm_locked-thp.patch
