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authorKairui Song <kasong@tencent.com>2022-12-20 02:58:37 +0800
committerAndrew Morton <akpm@linux-foundation.org>2023-01-18 17:12:44 -0800
commit3f79b187ad2f677047a1f1104bfb8a81b58b67d5 (patch)
treec8e8abd6d245bc1efbc633c6e449e7828dcce950 /mm/swapfile.c
parent497b099d9a166f819e667f4bf258e7a00ea2e78a (diff)
downloadlinux-next-3f79b187ad2f677047a1f1104bfb8a81b58b67d5.tar.gz
swapfile: get rid of volatile and avoid redundant read
Patch series "Clean up and fixes for swap", v2. This series cleans up some code paths, saves a few cycles and reduces the object size by a bit. It also fixes some rare race issue with statistics. This patch (of 4): Convert a volatile variable to more readable READ_ONCE. And this actually avoids the code from reading the variable twice redundantly when it races. Link: https://lkml.kernel.org/r/20221219185840.25441-1-ryncsn@gmail.com Link: https://lkml.kernel.org/r/20221219185840.25441-2-ryncsn@gmail.com Signed-off-by: Kairui Song <kasong@tencent.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 908a529bca12..6d3f60bd383b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1835,13 +1835,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
pte_t *pte;
struct swap_info_struct *si;
int ret = 0;
- volatile unsigned char *swap_map;
si = swap_info[type];
pte = pte_offset_map(pmd, addr);
do {
struct folio *folio;
unsigned long offset;
+ unsigned char swp_count;
if (!is_swap_pte(*pte))
continue;
@@ -1852,7 +1852,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
offset = swp_offset(entry);
pte_unmap(pte);
- swap_map = &si->swap_map[offset];
folio = swap_cache_get_folio(entry, vma, addr);
if (!folio) {
struct page *page;
@@ -1869,8 +1868,10 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
folio = page_folio(page);
}
if (!folio) {
- if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)
+ swp_count = READ_ONCE(si->swap_map[offset]);
+ if (swp_count == 0 || swp_count == SWAP_MAP_BAD)
goto try_next;
+
return -ENOMEM;
}