mm, swap: avoid redundant swap device pinning

Currently __read_swap_cache_async() has get/put_swap_device() calls to
increase/decrease a swap device reference to prevent swapoff.  While some
of its callers have already held the swap device reference, e.g in
do_swap_page() and shmem_swapin_folio() where __read_swap_cache_async()
will finally called.  Now there are only two callers not holding a swap
device reference, so make them hold a reference instead.  And drop the
get/put_swap_device calls in __read_swap_cache_async.  This should reduce
the overhead for swap in during page fault slightly.

Link: https://lkml.kernel.org/r/20250313165935.63303-4-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swap_state.c b/mm/swap_state.c
index a54b035d6a6cc532dad46e9d12a4682a0d92d958..50840a2887a518f01ced1497217a7f7e00469ab5 100644 (file)
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -426,17 +426,13 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
                bool skip_if_exists)
 {
-       struct swap_info_struct *si;
+       struct swap_info_struct *si = swp_swap_info(entry);
        struct folio *folio;
        struct folio *new_folio = NULL;
        struct folio *result = NULL;
        void *shadow = NULL;
 
        *new_page_allocated = false;
-       si = get_swap_device(entry);
-       if (!si)
-               return NULL;
-
        for (;;) {
                int err;
                /*
@@ -532,7 +528,6 @@ fail_unlock:
        put_swap_folio(new_folio, entry);
        folio_unlock(new_folio);
 put_and_return:
-       put_swap_device(si);
        if (!(*new_page_allocated) && new_folio)
                folio_put(new_folio);
        return result;
@@ -552,11 +547,16 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                struct vm_area_struct *vma, unsigned long addr,
                struct swap_iocb **plug)
 {
+       struct swap_info_struct *si;
        bool page_allocated;
        struct mempolicy *mpol;
        pgoff_t ilx;
        struct folio *folio;
 
+       si = get_swap_device(entry);
+       if (!si)
+               return NULL;
+
        mpol = get_vma_policy(vma, addr, 0, &ilx);
        folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
                                        &page_allocated, false);
@@ -564,6 +564,8 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 
        if (page_allocated)
                swap_read_folio(folio, plug);
+
+       put_swap_device(si);
        return folio;
 }
 

diff --git a/mm/zswap.c b/mm/zswap.c
index 23365e76a3ce37579d32b70a4016e1bc3a5cb5d4..8a1ded8fa97310c5f77c394b8f27ad14225a0ac4 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1051,14 +1051,20 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
        struct folio *folio;
        struct mempolicy *mpol;
        bool folio_was_allocated;
+       struct swap_info_struct *si;
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_NONE,
        };
 
        /* try to allocate swap cache folio */
+       si = get_swap_device(swpentry);
+       if (!si)
+               return -EEXIST;
+
        mpol = get_task_policy(current);
        folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
-                               NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
+                       NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
+       put_swap_device(si);
        if (!folio)
                return -ENOMEM;