The patch titled
Subject: mm: clarify swap_count_continued and improve readability for __swap_duplicate
has been added to the -mm mm-unstable branch. Its filename is
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-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: Barry Song <v-songbaohua@xxxxxxxx>
Subject: mm: clarify swap_count_continued and improve readability for __swap_duplicate
Date: Fri, 2 Aug 2024 17:52:43 +1200
When usage=1 and swapcount is very large, the situation can become quite
complex. The first entry might succeed with swap_count_continued(), but
the second entry may require extending to an additional continued page.
Rolling back these changes can be extremely challenging. Therefore,
anyone using usage==1 for batched __swap_duplicate() operations should
proceed with caution.
Additionally, we have moved swap_count_continued() to the second iteration
to enhance readability, as this function may modify data.
Link: https://lkml.kernel.org/r/20240802071817.47081-1-21cnbao@xxxxxxxxx
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Gao Xiang <xiang@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 38 +++++++++++++++++---------------------
1 file changed, 17 insertions(+), 21 deletions(-)
--- a/mm/swapfile.c~mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-fix
+++ a/mm/swapfile.c
@@ -3386,6 +3386,7 @@ static int __swap_duplicate(swp_entry_t
offset = swp_offset(entry);
VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
+ VM_WARN_ON(usage == 1 && nr > 1);
ci = lock_cluster_or_swap_info(p, offset);
err = 0;
@@ -3404,27 +3405,14 @@ static int __swap_duplicate(swp_entry_t
has_cache = count & SWAP_HAS_CACHE;
count &= ~SWAP_HAS_CACHE;
- if (usage == SWAP_HAS_CACHE) {
- /* set SWAP_HAS_CACHE if there is no cache and entry is used */
- if (!has_cache && count)
- continue;
- else if (has_cache) /* someone else added cache */
+ if (!count && !has_cache) {
+ err = -ENOENT;
+ } else if (usage == SWAP_HAS_CACHE) {
+ if (has_cache)
err = -EEXIST;
- else /* no users remaining */
- err = -ENOENT;
-
- } else if (count || has_cache) {
-
- if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
- continue;
- else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
- err = -EINVAL;
- else if (swap_count_continued(p, offset + i, count))
- continue;
- else
- err = -ENOMEM;
- } else
- err = -ENOENT; /* unused swap entry */
+ } else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) {
+ err = -EINVAL;
+ }
if (err)
goto unlock_out;
@@ -3439,8 +3427,16 @@ static int __swap_duplicate(swp_entry_t
has_cache = SWAP_HAS_CACHE;
else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
count += usage;
- else
+ else if (swap_count_continued(p, offset + i, count))
count = COUNT_CONTINUED;
+ else {
+ /*
+ * Don't need to rollback changes, because if
+ * usage == 1, there must be nr == 1.
+ */
+ err = -ENOMEM;
+ goto unlock_out;
+ }
WRITE_ONCE(p->swap_map[offset + i], count | has_cache);
}
_
Patches currently in -mm which might be from v-songbaohua@xxxxxxxx are
mm-extend-usage-parameter-so-that-cluster_swap_free_nr-can-be-reused.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-fix.patch
vpda-try-to-fix-the-potential-crash-due-to-misusing-__gfp_nofail.patch
mm-document-__gfp_nofail-must-be-blockable.patch
mm-bug_on-to-avoid-null-deference-while-__gfp_nofail-fails.patch
mm-prohibit-null-deference-exposed-for-unsupported-non-blockable-__gfp_nofail.patch
mm-add-nr-argument-in-mem_cgroup_swapin_uncharge_swap-helper-to-support-large-folios.patch
