The patch titled
Subject: Re: mm: filemap: use xa_get_order() to get the swap entry order
has been added to the -mm mm-unstable branch. Its filename is
mm-filemap-use-xa_get_order-to-get-the-swap-entry-order-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-filemap-use-xa_get_order-to-get-the-swap-entry-order-fix.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: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: Re: mm: filemap: use xa_get_order() to get the swap entry order
Date: Thu, 29 Aug 2024 01:07:17 -0700 (PDT)
find_lock_entries(), used in the first pass of shmem_undo_range() and
truncate_inode_pages_range() before partial folios are dealt with, has to
be careful to avoid those partial folios: as its doc helpfully says,
"Folios which are partially outside the range are not returned". Of
course, the same must be true of any value entries returned, otherwise
truncation and hole-punch risk erasing swapped areas - as has been seen.
Rewrite find_lock_entries() to emphasize that, following the same pattern
for folios and for value entries.
Adjust find_get_entries() slightly, to get order while still holding
rcu_read_lock(), and to round down the updated start: good changes, like
find_lock_entries() now does, but it's unclear if either is ever
important.
Link: https://lkml.kernel.org/r/c336e6e4-da7f-b714-c0f1-12df715f2611@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 41 +++++++++++++++++++++++++----------------
1 file changed, 25 insertions(+), 16 deletions(-)
--- a/mm/filemap.c~mm-filemap-use-xa_get_order-to-get-the-swap-entry-order-fix
+++ a/mm/filemap.c
@@ -2046,10 +2046,9 @@ unsigned find_get_entries(struct address
if (!folio_batch_add(fbatch, folio))
break;
}
- rcu_read_unlock();
if (folio_batch_count(fbatch)) {
- unsigned long nr = 1;
+ unsigned long nr;
int idx = folio_batch_count(fbatch) - 1;
folio = fbatch->folios[idx];
@@ -2057,8 +2056,10 @@ unsigned find_get_entries(struct address
nr = folio_nr_pages(folio);
else
nr = 1 << xa_get_order(&mapping->i_pages, indices[idx]);
- *start = indices[idx] + nr;
+ *start = round_down(indices[idx] + nr, nr);
}
+ rcu_read_unlock();
+
return folio_batch_count(fbatch);
}
@@ -2090,10 +2091,17 @@ unsigned find_lock_entries(struct addres
rcu_read_lock();
while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
+ unsigned long base;
+ unsigned long nr;
+
if (!xa_is_value(folio)) {
- if (folio->index < *start)
+ nr = folio_nr_pages(folio);
+ base = folio->index;
+ /* Omit large folio which begins before the start */
+ if (base < *start)
goto put;
- if (folio_next_index(folio) - 1 > end)
+ /* Omit large folio which extends beyond the end */
+ if (base + nr - 1 > end)
goto put;
if (!folio_trylock(folio))
goto put;
@@ -2102,7 +2110,19 @@ unsigned find_lock_entries(struct addres
goto unlock;
VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
folio);
+ } else {
+ nr = 1 << xa_get_order(&mapping->i_pages, xas.xa_index);
+ base = xas.xa_index & ~(nr - 1);
+ /* Omit order>0 value which begins before the start */
+ if (base < *start)
+ continue;
+ /* Omit order>0 value which extends beyond the end */
+ if (base + nr - 1 > end)
+ break;
}
+
+ /* Update start now so that last update is correct on return */
+ *start = base + nr;
indices[fbatch->nr] = xas.xa_index;
if (!folio_batch_add(fbatch, folio))
break;
@@ -2114,17 +2134,6 @@ put:
}
rcu_read_unlock();
- if (folio_batch_count(fbatch)) {
- unsigned long nr = 1;
- int idx = folio_batch_count(fbatch) - 1;
-
- folio = fbatch->folios[idx];
- if (!xa_is_value(folio))
- nr = folio_nr_pages(folio);
- else
- nr = 1 << xa_get_order(&mapping->i_pages, indices[idx]);
- *start = indices[idx] + nr;
- }
return folio_batch_count(fbatch);
}
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-attempt-to-batch-free-swap-entries-for-zap_pte_range-fix-2.patch
mm-filemap-use-xa_get_order-to-get-the-swap-entry-order-fix.patch
mm-shmem-split-large-entry-if-the-swapin-folio-is-not-large-fix.patch
mm-shmem-support-large-folio-swap-out-fix.patch
mm-restart-if-multiple-traversals-raced-fix.patch
mm-shmem-fix-minor-off-by-one-in-shrinkable-calculation.patch
mm-shmem-extend-shmem_unused_huge_shrink-to-all-sizes.patch
