The patch titled
Subject: mm: truncate: split huge page cache page to a non-zero order if possible
has been added to the -mm mm-unstable branch. Its filename is
mm-truncate-split-huge-page-cache-page-to-a-non-zero-order-if-possible.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-truncate-split-huge-page-cache-page-to-a-non-zero-order-if-possible.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
Subject: mm: truncate: split huge page cache page to a non-zero order if possible
Date: Mon, 3 Apr 2023 16:18:38 -0400
To minimize the number of pages after a huge page truncation, we do not
need to split it all the way down to order-0. The huge page has at most
three parts, the part before offset, the part to be truncated, the part
remaining at the end. Find the greatest common divisor of them to
calculate the new page order from it, so we can split the huge page to
this order and keep the remaining pages as large and as few as possible.
Link: https://lkml.kernel.org/r/20230403201839.4097845-7-zi.yan@xxxxxxxx
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/truncate.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
--- a/mm/truncate.c~mm-truncate-split-huge-page-cache-page-to-a-non-zero-order-if-possible
+++ a/mm/truncate.c
@@ -22,6 +22,7 @@
#include <linux/buffer_head.h> /* grr. try_to_release_page */
#include <linux/shmem_fs.h>
#include <linux/rmap.h>
+#include <linux/gcd.h>
#include "internal.h"
/*
@@ -211,7 +212,8 @@ int truncate_inode_folio(struct address_
bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
{
loff_t pos = folio_pos(folio);
- unsigned int offset, length;
+ unsigned int offset, length, remaining;
+ unsigned int new_order = folio_order(folio);
if (pos < start)
offset = start - pos;
@@ -222,6 +224,7 @@ bool truncate_inode_partial_folio(struct
length = length - offset;
else
length = end + 1 - pos - offset;
+ remaining = folio_size(folio) - offset - length;
folio_wait_writeback(folio);
if (length == folio_size(folio)) {
@@ -236,11 +239,25 @@ bool truncate_inode_partial_folio(struct
*/
folio_zero_range(folio, offset, length);
+ /*
+ * Use the greatest common divisor of offset, length, and remaining
+ * as the smallest page size and compute the new order from it. So we
+ * can truncate a subpage as large as possible. Round up gcd to
+ * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0.
+ */
+ new_order = ilog2(round_up(gcd(gcd(offset, length), remaining),
+ PAGE_SIZE) / PAGE_SIZE);
+
+ /* order-1 THP not supported, downgrade to order-0 */
+ if (new_order == 1)
+ new_order = 0;
+
+
if (folio_has_private(folio))
folio_invalidate(folio, offset, length);
if (!folio_test_large(folio))
return true;
- if (split_folio(folio) == 0)
+ if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0)
return true;
if (folio_test_dirty(folio))
return false;
_
Patches currently in -mm which might be from ziy@xxxxxxxxxx are
mm-memcg-use-order-instead-of-nr-in-split_page_memcg.patch
mm-page_owner-use-order-instead-of-nr-in-split_page_owner.patch
mm-memcg-make-memcg-huge-page-split-support-any-order-split.patch
mm-page_owner-add-support-for-splitting-to-any-order-in-split-page_owner.patch
mm-thp-split-huge-page-to-any-lower-order-pages.patch
mm-truncate-split-huge-page-cache-page-to-a-non-zero-order-if-possible.patch
mm-huge_memory-enable-debugfs-to-split-huge-pages-to-any-order.patch
