The patch titled
Subject: mm/thp: flush file for !is_shmem PageDirty() case in collapse_file()
has been added to the -mm tree. Its filename is
mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch
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------------------------------------------------------
From: Song Liu <songliubraving@xxxxxx>
Subject: mm/thp: flush file for !is_shmem PageDirty() case in collapse_file()
For non-shmem file THPs, khugepaged only collapses read only .text mapping
(VM_DENYWRITE). These pages should not be dirty except the case where the
file hasn't been flushed since first write.
Call filemap_flush() in collapse_file() to accelerate the write back in
such cases.
Link: http://lkml.kernel.org/r/20191106060930.2571389-3-songliubraving@xxxxxx
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
--- a/mm/khugepaged.c~mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file
+++ a/mm/khugepaged.c
@@ -1602,6 +1602,24 @@ static void collapse_file(struct mm_stru
result = SCAN_FAIL;
goto xa_unlocked;
}
+ } else if (PageDirty(page)) {
+ /*
+ * khugepaged only works on read-only fd,
+ * so this page is dirty because it hasn't
+ * been flushed since first write. There
+ * won't be new dirty pages.
+ *
+ * Trigger async flush here and hope the
+ * writeback is done when khugepaged
+ * revisits this page.
+ *
+ * This is a one-off situation. We are not
+ * forcing writeback in loop.
+ */
+ xas_unlock_irq(&xas);
+ filemap_flush(mapping);
+ result = SCAN_FAIL;
+ goto xa_unlocked;
} else if (trylock_page(page)) {
get_page(page);
xas_unlock_irq(&xas);
_
Patches currently in -mm which might be from songliubraving@xxxxxx are
mmthp-recheck-each-page-before-collapsing-file-thp.patch
mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch
