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Mon, 24 Feb 2025 10:03:01 -0800 (PST) From: Kairui Song To: linux-mm@kvack.org Cc: Andrew Morton , Chris Li , Barry Song , Hugh Dickins , Yosry Ahmed , "Huang, Ying" , Baoquan He , Nhat Pham , Johannes Weiner , Baolin Wang , Kalesh Singh , Matthew Wilcox , linux-kernel@vger.kernel.org, Kairui Song Subject: [PATCH v2 3/7] mm, swap: avoid redundant swap device pinning Date: Tue, 25 Feb 2025 02:02:08 +0800 Message-ID: <20250224180212.22802-4-ryncsn@gmail.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250224180212.22802-1-ryncsn@gmail.com> References: <20250224180212.22802-1-ryncsn@gmail.com> Reply-To: Kairui Song Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Kairui Song 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. Signed-off-by: Kairui Song Reviewed-by: Baoquan He --- mm/swap_state.c | 14 ++++++++------ mm/zswap.c | 6 ++++++ 2 files changed, 14 insertions(+), 6 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index a54b035d6a6c..50840a2887a5 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -426,17 +426,13 @@ struct folio *__read_swap_cache_async(swp_entry_t ent= ry, 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 =3D swp_swap_info(entry); struct folio *folio; struct folio *new_folio =3D NULL; struct folio *result =3D NULL; void *shadow =3D NULL; =20 *new_page_allocated =3D false; - si =3D get_swap_device(entry); - if (!si) - return NULL; - for (;;) { int err; /* @@ -532,7 +528,6 @@ struct folio *__read_swap_cache_async(swp_entry_t entry= , gfp_t gfp_mask, 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; =20 + si =3D get_swap_device(entry); + if (!si) + return NULL; + mpol =3D get_vma_policy(vma, addr, 0, &ilx); folio =3D __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, =20 if (page_allocated) swap_read_folio(folio, plug); + + put_swap_device(si); return folio; } =20 diff --git a/mm/zswap.c b/mm/zswap.c index ac9d299e7d0c..83dfa1f9e689 100644 --- 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 =3D { .sync_mode =3D WB_SYNC_NONE, }; =20 /* try to allocate swap cache folio */ + si =3D get_swap_device(swpentry); + if (!si) + return -EEXIST; + mpol =3D get_task_policy(current); folio =3D __read_swap_cache_async(swpentry, GFP_KERNEL, mpol, NO_INTERLEAVE_INDEX, &folio_was_allocated, true); + put_swap_device(si); if (!folio) return -ENOMEM; =20 --=20 2.48.1