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Sun, 08 Feb 2026 13:58:53 -0800 (PST) Received: from localhost ([2a03:2880:10ff:73::]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-66d3adcae3csm5051168eaf.9.2026.02.08.13.58.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Feb 2026 13:58:52 -0800 (PST) From: Nhat Pham To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, yosry.ahmed@linux.dev, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, len.brown@intel.com, chengming.zhou@linux.dev, kasong@tencent.com, chrisl@kernel.org, huang.ying.caritas@gmail.com, ryan.roberts@arm.com, shikemeng@huaweicloud.com, viro@zeniv.linux.org.uk, baohua@kernel.org, bhe@redhat.com, osalvador@suse.de, lorenzo.stoakes@oracle.com, christophe.leroy@csgroup.eu, pavel@kernel.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-pm@vger.kernel.org, peterx@redhat.com, riel@surriel.com, joshua.hahnjy@gmail.com, npache@redhat.com, gourry@gourry.net, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rafael@kernel.org, jannh@google.com, pfalcato@suse.de, zhengqi.arch@bytedance.com Subject: [PATCH v3 05/20] mm/swap: add a new function to check if a swap entry is in swap cached. Date: Sun, 8 Feb 2026 13:58:18 -0800 Message-ID: <20260208215839.87595-6-nphamcs@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260208215839.87595-1-nphamcs@gmail.com> References: <20260208215839.87595-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: m4hkdkxsxda6swmzocoiywddsic3ijpq X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 2AA1318000E X-HE-Tag: 1770587933-306648 X-HE-Meta: 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 t0JhdkRo 5AQANY8z4KzVi4yMbjtHuBipAPzgl3ZZAXqFDYRJULtlhcUjKJtLgLvbUdXc9Mq5SC9QrRPq3iIk92QcbueoEsPUbPyFPYDH2vXJGEMv73GqUC1QqZesFI/bMFBzQqOL1VhIwvrqBwXzL/CY2JR3YYdON0HTm+6Klhi3O0lDvWOdPGiKt4+FY4cdNqDY79xAT9pA044Xs2YuhqlGnggVpC7pjS7IdGD/tHnoy/Jo3aZ5ch/SgN3rrrRCvZtBOAQG01o5SqmUHdJ+38hA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Userfaultfd checks whether a swap entry is in swapcache. This is currently done by directly looking at the swapfile's swap map - however, the swap cached state will soon be managed at the virtual swap layer. Abstract away this function. Signed-off-by: Nhat Pham --- include/linux/swap.h | 6 ++++++ mm/swapfile.c | 15 +++++++++++++++ mm/userfaultfd.c | 3 +-- 3 files changed, 22 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 3da637b218baf..f91a442ac0e82 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -435,6 +435,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr); int __swap_count(swp_entry_t entry); bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry); int swp_swapcount(swp_entry_t entry); +bool is_swap_cached(swp_entry_t entry); /* Swap cache API (mm/swap_state.c) */ static inline unsigned long total_swapcache_pages(void) @@ -554,6 +555,11 @@ static inline int swp_swapcount(swp_entry_t entry) return 0; } +static inline bool is_swap_cached(swp_entry_t entry) +{ + return false; +} + static inline int folio_alloc_swap(struct folio *folio) { return -EINVAL; diff --git a/mm/swapfile.c b/mm/swapfile.c index cacfafa9a540d..3c89dedbd5718 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -194,6 +194,21 @@ static bool swap_only_has_cache(struct swap_info_struct *si, return true; } +/** + * is_swap_cached - check if the swap entry is cached + * @entry: swap entry to check + * + * Check swap_map directly to minimize overhead, READ_ONCE is sufficient. + * + * Returns true if the swap entry is cached, false otherwise. + */ +bool is_swap_cached(swp_entry_t entry) +{ + struct swap_info_struct *si = __swap_entry_to_info(entry); + + return READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE; +} + static bool swap_is_last_map(struct swap_info_struct *si, unsigned long offset, int nr_pages, bool *has_cache) { diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 25f89eba0438c..98be764fb3ecd 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1190,7 +1190,6 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, * Check if the swap entry is cached after acquiring the src_pte * lock. Otherwise, we might miss a newly loaded swap cache folio. * - * Check swap_map directly to minimize overhead, READ_ONCE is sufficient. * We are trying to catch newly added swap cache, the only possible case is * when a folio is swapped in and out again staying in swap cache, using the * same entry before the PTE check above. The PTL is acquired and released @@ -1200,7 +1199,7 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, * cache, or during the tiny synchronization window between swap cache and * swap_map, but it will be gone very quickly, worst result is retry jitters. */ - if (READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE) { + if (is_swap_cached(entry)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } -- 2.47.3