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authorHugh Dickins <hughd@google.com>2022-02-15 05:40:55 +0300
committerMatthew Wilcox (Oracle) <willy@infradead.org>2022-02-17 19:59:45 +0300
commit6d9df8a5889c569ab9e3bcb38b12e5b81b6b9bde (patch)
tree027372c9efe3f64cb5fbee730449c88c02c451f3 /mm/khugepaged.c
parentb74355078b6554271371532a5daa3b1a3db620f9 (diff)
downloadlinux-6d9df8a5889c569ab9e3bcb38b12e5b81b6b9bde.tar.xz
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. Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 52add1825525..fa05e6d39783 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1834,13 +1834,12 @@ static void collapse_file(struct mm_struct *mm,
}
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:
@@ -1904,6 +1903,13 @@ 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;