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mm, swap: no need to clear the shadow explicitly

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Since we no longer bypass the swap cache, every swap-in will clear the
swap shadow by inserting the folio into the swap table.  The only place we
may seem to need to free the swap shadow is when the swap slots are freed
directly without a folio (swap_put_entries_direct).  But with the swap
table, that is not needed either.  Freeing a slot in the swap table will
set the table entry to NULL, which erases the shadow just fine.

So just delete all explicit shadow clearing, it's no longer needed.  Also,
rearrange the freeing.

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-12-f4e34be021a7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kairui Song
2026-02-18 04:06:37 +08:00
committed by Andrew Morton
parent a0f79916e1
commit 1df1a1b950
3 changed files with 0 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
mm/swap.h
View File

@@ -290,7 +290,6 @@ void __swap_cache_del_folio(struct swap_cluster_info *ci,
struct folio *folio, swp_entry_t entry, void *shadow);
void __swap_cache_replace_folio(struct swap_cluster_info *ci,
struct folio *old, struct folio *new);
void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents);
void show_swap_cache_info(void);
void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);

21
mm/swap_state.c
View File

@@ -350,27 +350,6 @@ void __swap_cache_replace_folio(struct swap_cluster_info *ci,
}
}
/**
* __swap_cache_clear_shadow - Clears a set of shadows in the swap cache.
* @entry: The starting index entry.
* @nr_ents: How many slots need to be cleared.
*
* Context: Caller must ensure the range is valid, all in one single cluster,
* not occupied by any folio, and lock the cluster.
*/
void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents)
{
struct swap_cluster_info *ci = __swap_entry_to_cluster(entry);
unsigned int ci_off = swp_cluster_offset(entry), ci_end;
unsigned long old;
ci_end = ci_off + nr_ents;
do {
old = __swap_table_xchg(ci, ci_off, null_to_swp_tb());
WARN_ON_ONCE(swp_tb_is_folio(old) || swp_tb_get_count(old));
} while (++ci_off < ci_end);
}
/*
* If we are the only user, then try to free up the swap cache.
*

2
mm/swapfile.c
View File

@@ -1287,7 +1287,6 @@ static void swap_range_alloc(struct swap_info_struct *si,
static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
unsigned int nr_entries)
{
unsigned long begin = offset;
unsigned long end = offset + nr_entries - 1;
void (*swap_slot_free_notify)(struct block_device *, unsigned long);
unsigned int i;
@@ -1312,7 +1311,6 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
swap_slot_free_notify(si->bdev, offset);
offset++;
}
__swap_cache_clear_shadow(swp_entry(si->type, begin), nr_entries);
/*
* Make sure that try_to_unuse() observes si->inuse_pages reaching 0