The patch titled
Subject: swap: avoid holding swap reference in swap_cache_get_folio
has been added to the -mm mm-unstable branch. Its filename is
swap-avoid-holding-swap-reference-in-swap_cache_get_folio.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/swap-avoid-holding-swap-reference-in-swap_cache_get_folio.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: Kairui Song <kasong@xxxxxxxxxxx>
Subject: swap: avoid holding swap reference in swap_cache_get_folio
Date: Tue, 20 Dec 2022 02:58:40 +0800
All its callers either already hold a reference to, or lock the swap
device while calling this function. There is only one exception in
shmem_swapin_folio, just make this caller also hold a reference of the
swap device, so this helper can be simplified and saves a few cycles.
This also provides finer control of error handling in shmem_swapin_folio,
on race (with swap off), it can just try again. For invalid swap entry,
it can fail with a proper error code.
Link: https://lkml.kernel.org/r/20221219185840.25441-5-ryncsn@xxxxxxxxx
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 11 +++++++++++
mm/swap_state.c | 8 ++------
2 files changed, 13 insertions(+), 6 deletions(-)
--- a/mm/shmem.c~swap-avoid-holding-swap-reference-in-swap_cache_get_folio
+++ a/mm/shmem.c
@@ -1741,6 +1741,7 @@ static int shmem_swapin_folio(struct ino
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info = SHMEM_I(inode);
struct mm_struct *charge_mm = vma ? vma->vm_mm : NULL;
+ struct swap_info_struct *si;
struct folio *folio = NULL;
swp_entry_t swap;
int error;
@@ -1752,6 +1753,14 @@ static int shmem_swapin_folio(struct ino
if (is_swapin_error_entry(swap))
return -EIO;
+ si = get_swap_device(swap);
+ if (!si) {
+ if (!shmem_confirm_swap(mapping, index, swap))
+ return -EEXIST;
+ else
+ return -EINVAL;
+ }
+
/* Look it up and read it in.. */
folio = swap_cache_get_folio(swap, NULL, 0);
if (!folio) {
@@ -1812,6 +1821,7 @@ static int shmem_swapin_folio(struct ino
delete_from_swap_cache(folio);
folio_mark_dirty(folio);
swap_free(swap);
+ put_swap_device(si);
*foliop = folio;
return 0;
@@ -1825,6 +1835,7 @@ unlock:
folio_unlock(folio);
folio_put(folio);
}
+ put_swap_device(si);
return error;
}
--- a/mm/swap_state.c~swap-avoid-holding-swap-reference-in-swap_cache_get_folio
+++ a/mm/swap_state.c
@@ -321,19 +321,15 @@ static inline bool swap_use_vma_readahea
* unlocked and with its refcount incremented - we rely on the kernel
* lock getting page table operations atomic even if we drop the folio
* lock before returning.
+ *
+ * Caller must lock the swap device or hold a reference to keep it valid.
*/
struct folio *swap_cache_get_folio(swp_entry_t entry,
struct vm_area_struct *vma, unsigned long addr)
{
struct folio *folio;
- struct swap_info_struct *si;
- si = get_swap_device(entry);
- if (!si)
- return NULL;
folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
- put_swap_device(si);
-
if (folio) {
bool vma_ra = swap_use_vma_readahead();
bool readahead;
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
swapfile-get-rid-of-volatile-and-avoid-redundant-read.patch
swap-avoid-a-redundant-pte-map-if-ra-window-is-1.patch
swap-fold-swap_ra_clamp_pfn-into-swap_ra_info.patch
swap-avoid-holding-swap-reference-in-swap_cache_get_folio.patch
