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swap: avoid holding swap reference in swap_cache_get_folio 

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@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.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>
This commit is contained in:
Kairui Song 2022-12-20 02:58:40 +08:00 committed by Andrew Morton
parent 16ba391e9c
commit cbc2bd98db
2 changed files with 13 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
mm/shmem.c
View File

@ -1739,6 +1739,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
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;
@ -1750,6 +1751,14 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
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) {
@ -1810,6 +1819,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
delete_from_swap_cache(folio);
folio_mark_dirty(folio);
swap_free(swap);
put_swap_device(si);
*foliop = folio;
return 0;
@ -1823,6 +1833,7 @@ unlock:
folio_unlock(folio);
folio_put(folio);
}
put_swap_device(si);
return error;
}

8
mm/swap_state.c
View File

@ -321,19 +321,15 @@ static inline bool swap_use_vma_readahead(void)
* 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;