From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f178.google.com (mail-qk1-f178.google.com [209.85.222.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7025A311972 for ; Sun, 16 Nov 2025 18:12:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763316771; cv=none; b=u5FXnZgJIQZQygg4uYHK4ho4in0Pkf6eY65jLg82ECev4HIfGMjJ/Z5dIeBfpPFwPan3x8kfK4Gk/rerjuMeVfyA5fsX3YfpipA4ULAMH2vEYlURxCuCdifbftXwktPwYvwsUCMi+MMnOdETcM2UOuCXHj95ED3XWikq95f4OJA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763316771; c=relaxed/simple; bh=b6YLQma/xhgohts91m9URbFvnK4lni8QBuGf9q+0nAk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=R2Si6Q+Oc9+i2Cjv1MwwasSlc72Bc4YVWqZtXRXPMGN+ocV1RGuiYznbsEHDIro6yyn44DaJsJ2VrdE9Y5nZ9TaTUNt2ODnyV7uyBvuRjwXrFZFIpRiOYWlmmg/Pmoap+453PBplcEZrPG46G59ooQR5NiwotcRu9scPbI/C7z4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=RsroYcg6; arc=none smtp.client-ip=209.85.222.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RsroYcg6" Received: by mail-qk1-f178.google.com with SMTP id af79cd13be357-8b2dec4d115so107763085a.0 for ; Sun, 16 Nov 2025 10:12:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1763316768; x=1763921568; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=q7cVKpKHZH//zr8S57LiQqEN2eoJht/6Q46RrkqejeE=; b=RsroYcg6vU0YF5GGU5SLQOMhS0RgFSgaW9W5KyHLKwSAwFNFj4i51R1HkiGaJDF8Vq zqvEDfaWgHC2W0b8REA9rZJS3f8UPvPO6+OLjbtWFlAdaxqEis4TQUrifiMP2+imXg7h uy8fwOtPELFfwiwYrC+ay9ZXIOV7Vhookd3vk58aLa6QocHyAvntq5iPMNSb9AHRvTt4 EX5smA9WLGNJGjZojBIfTuzBRqOZ10sKJvCEN1FWqrwCE+aLWZ3JKbzXCjcsdzdo4bay WysSE6ruG1PzUYT5nmriuyDt0Q+RPdBEpYwulh8oBBDX7BKu82q1Af4hiruHkygVyqrS rJjA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1763316768; x=1763921568; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-gg:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=q7cVKpKHZH//zr8S57LiQqEN2eoJht/6Q46RrkqejeE=; b=Ww0zJ6aDCO7WGBSObMNYlBTDxlIGfqpJl7JSWsgFzN1UB3eVX6FbfhbqdKO8CjndUG 8tRlycQAOKr9fAfQncPjGMV8VqQcJrm6n+cPx/Pm6euSlyHrFtWXBw7sEo95VOe+6vDy qcZMmFfh+zIf0n7ZM5MxcRGjY/U+SJ68BFD08OYvsSVFRkTYc5i7LcxE+/boB7L6G3zu Y3/ISkHd6UoVd7TqHWzx8q/tHxD2bf5fSCi7lXBu27sNs9OMfdlHhJmsGWlCcdBZRp2W nYTxDNI3iYFo2KrCHeXEORXEgctP0vhUzwY5S0Q27jywYCpLyOu3MonTizhNE2Y/3ggN RQ9A== X-Forwarded-Encrypted: i=1; AJvYcCVffhdEcx5GZ2ti+UALat/3O/zrGJlEL/ZCINr1xjXBFDGk7WvrQSOUPJ6UZrkVcm5gsoCR+jh8xtWl8rY=@vger.kernel.org X-Gm-Message-State: AOJu0YzP+5liUh5wistiH5p8OIaoYUL8p7mEGOTPm/9b9JCq1vX30ijE Vre/hf8x/bOrZw7xSNJDSrgl/4fx5lt+jQf/RZ87PyJN6H+Vat1Qywf0 X-Gm-Gg: ASbGncsY7zoMpozCbUmobyCnbEjI37sk78P4G48VuuIWDWdXYaHw+ZviRDOm7/+uykO 9ANa+7l2RO3OUdMUHdPu4FH4UNhnvoNa5zZZTpH5YU5hfYizcVa9ND5ui6wi/8T4KCZ8ka48seB 27xgBsAsq6RQVcwNq4da3pFAXAR8H3ga9LAsdxmetHlNy1y+0pRSOEK8W2W1pCEB8iB+dJQCUVX e3hcjAdf9GPq6SPifNKOSClnKOmRqsP5muLcgOAcOrKap06uJsLGhJqkxKpVK99xu2csPXvbFaL qBXkFLrT/tMp671GLDOJ65P3IDgOHxVho1DH36xX6Z5W/6WaOdICWEvZvW8bl9uRclE4f2U/Wum lXcZt7pGvn6uSml0VcmU+9PVdI/iYM8lUSXq4c+QSiERxW6f4rPlzM5wRAf4BmgEXi/uKt9obnb 2r3e1GekwjCQ0LtJqYzVLHXR54aIxL2V8k3hdA+CsYZQ== X-Google-Smtp-Source: AGHT+IGUrKl+PzZ0iZ4xoM4cTBU/LuuyfiZTHx/WuGLuLNWgLxgoroAzxxcfWBHeqXQPGrcdxLF5iQ== X-Received: by 2002:a05:620a:1a02:b0:8b2:e924:4db7 with SMTP id af79cd13be357-8b2e924588emr238474985a.40.1763316768083; Sun, 16 Nov 2025 10:12:48 -0800 (PST) Received: from [127.0.0.1] ([101.32.222.185]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8b2e089b436sm305447785a.45.2025.11.16.10.12.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Nov 2025 10:12:47 -0800 (PST) From: Kairui Song Date: Mon, 17 Nov 2025 02:11:49 +0800 Subject: [PATCH v2 08/19] mm/shmem, swap: remove SWAP_MAP_SHMEM Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251117-swap-table-p2-v2-8-37730e6ea6d5@tencent.com> References: <20251117-swap-table-p2-v2-0-37730e6ea6d5@tencent.com> In-Reply-To: <20251117-swap-table-p2-v2-0-37730e6ea6d5@tencent.com> To: linux-mm@kvack.org Cc: Andrew Morton , Baoquan He , Barry Song , Chris Li , Nhat Pham , Yosry Ahmed , David Hildenbrand , Johannes Weiner , Youngjun Park , Hugh Dickins , Baolin Wang , Ying Huang , Kemeng Shi , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, Kairui Song X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1763316712; l=7126; i=kasong@tencent.com; s=kasong-sign-tencent; h=from:subject:message-id; bh=dny+SXWuyE8K8IiOt2sIszvBbGvpqP/hk6etEBD5hKg=; b=fV49ZBo98ttH/vcQHSgk1G7A+xp6sTNohz8hLqQKodxZHVkd6sIjzP90SLf+Fx591oGAtVZQ/ xppHv2AvP0VCwBuc/2MuqSCo0w8KO7WyaIl7VrHNfunmODkQu/auvAa X-Developer-Key: i=kasong@tencent.com; a=ed25519; pk=kCdoBuwrYph+KrkJnrr7Sm1pwwhGDdZKcKrqiK8Y1mI= From: Nhat Pham The SWAP_MAP_SHMEM state was introduced in the commit aaa468653b4a ("swap_info: note SWAP_MAP_SHMEM"), to quickly determine if a swap entry belongs to shmem during swapoff. However, swapoff has since been rewritten in the commit b56a2d8af914 ("mm: rid swapoff of quadratic complexity"). Now having swap count == SWAP_MAP_SHMEM value is basically the same as having swap count == 1, and swap_shmem_alloc() behaves analogously to swap_duplicate(). The only difference of note is that swap_shmem_alloc() does not check for -ENOMEM returned from __swap_duplicate(), but it is OK because shmem never re-duplicates any swap entry it owns. This will stil be safe if we use (batched) swap_duplicate() instead. This commit adds swap_duplicate_nr(), the batched variant of swap_duplicate(), and removes the SWAP_MAP_SHMEM state and the associated swap_shmem_alloc() helper to simplify the state machine (both mentally and in terms of actual code). We will also have an extra state/special value that can be repurposed (for swap entries that never gets re-duplicated). Signed-off-by: Nhat Pham Signed-off-by: Kairui Song --- include/linux/swap.h | 15 +++++++-------- mm/shmem.c | 2 +- mm/swapfile.c | 42 +++++++++++++++++------------------------- 3 files changed, 25 insertions(+), 34 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 38ca3df68716..bf72b548a96d 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -230,7 +230,6 @@ enum { /* Special value in first swap_map */ #define SWAP_MAP_MAX 0x3e /* Max count */ #define SWAP_MAP_BAD 0x3f /* Note page is bad */ -#define SWAP_MAP_SHMEM 0xbf /* Owned by shmem/tmpfs */ /* Special value in each swap_map continuation */ #define SWAP_CONT_MAX 0x7f /* Max count */ @@ -458,8 +457,7 @@ bool folio_free_swap(struct folio *folio); void put_swap_folio(struct folio *folio, swp_entry_t entry); extern swp_entry_t get_swap_page_of_type(int); extern int add_swap_count_continuation(swp_entry_t, gfp_t); -extern void swap_shmem_alloc(swp_entry_t, int); -extern int swap_duplicate(swp_entry_t); +extern int swap_duplicate_nr(swp_entry_t entry, int nr); extern int swapcache_prepare(swp_entry_t entry, int nr); extern void swap_free_nr(swp_entry_t entry, int nr_pages); extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); @@ -514,11 +512,7 @@ static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask) return 0; } -static inline void swap_shmem_alloc(swp_entry_t swp, int nr) -{ -} - -static inline int swap_duplicate(swp_entry_t swp) +static inline int swap_duplicate_nr(swp_entry_t swp, int nr_pages) { return 0; } @@ -569,6 +563,11 @@ static inline int add_swap_extent(struct swap_info_struct *sis, } #endif /* CONFIG_SWAP */ +static inline int swap_duplicate(swp_entry_t entry) +{ + return swap_duplicate_nr(entry, 1); +} + static inline void free_swap_and_cache(swp_entry_t entry) { free_swap_and_cache_nr(entry, 1); diff --git a/mm/shmem.c b/mm/shmem.c index 8b711b8bcdba..0b0af71ce5e8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1654,7 +1654,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug, spin_unlock(&shmem_swaplist_lock); } - swap_shmem_alloc(folio->swap, nr_pages); + swap_duplicate_nr(folio->swap, nr_pages); shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap)); BUG_ON(folio_mapped(folio)); diff --git a/mm/swapfile.c b/mm/swapfile.c index a433445e9225..580adf9d93bd 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -201,7 +201,7 @@ static bool swap_is_last_map(struct swap_info_struct *si, unsigned char *map_end = map + nr_pages; unsigned char count = *map; - if (swap_count(count) != 1 && swap_count(count) != SWAP_MAP_SHMEM) + if (swap_count(count) != 1) return false; while (++map < map_end) { @@ -1522,12 +1522,6 @@ static unsigned char swap_entry_put_locked(struct swap_info_struct *si, if (usage == SWAP_HAS_CACHE) { VM_BUG_ON(!has_cache); has_cache = 0; - } else if (count == SWAP_MAP_SHMEM) { - /* - * Or we could insist on shmem.c using a special - * swap_shmem_free() and free_shmem_swap_and_cache()... - */ - count = 0; } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) { if (count == COUNT_CONTINUED) { if (swap_count_continued(si, offset, count)) @@ -1625,7 +1619,7 @@ static bool swap_entries_put_map(struct swap_info_struct *si, if (nr <= 1) goto fallback; count = swap_count(data_race(si->swap_map[offset])); - if (count != 1 && count != SWAP_MAP_SHMEM) + if (count != 1) goto fallback; ci = swap_cluster_lock(si, offset); @@ -1679,12 +1673,10 @@ static bool swap_entries_put_map_nr(struct swap_info_struct *si, /* * Check if it's the last ref of swap entry in the freeing path. - * Qualified value includes 1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM. */ static inline bool __maybe_unused swap_is_last_ref(unsigned char count) { - return (count == SWAP_HAS_CACHE) || (count == 1) || - (count == SWAP_MAP_SHMEM); + return (count == SWAP_HAS_CACHE) || (count == 1); } /* @@ -3678,7 +3670,6 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) offset = swp_offset(entry); VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); - VM_WARN_ON(usage == 1 && nr > 1); ci = swap_cluster_lock(si, offset); err = 0; @@ -3738,27 +3729,28 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) return err; } -/* - * Help swapoff by noting that swap entry belongs to shmem/tmpfs - * (in which case its reference count is never incremented). - */ -void swap_shmem_alloc(swp_entry_t entry, int nr) -{ - __swap_duplicate(entry, SWAP_MAP_SHMEM, nr); -} - -/* - * Increase reference count of swap entry by 1. +/** + * swap_duplicate_nr() - Increase reference count of nr contiguous swap entries + * by 1. + * + * @entry: first swap entry from which we want to increase the refcount. + * @nr: Number of entries in range. + * * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required * but could not be atomically allocated. Returns 0, just as if it succeeded, * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which * might occur if a page table entry has got corrupted. + * + * Note that we are currently not handling the case where nr > 1 and we need to + * add swap count continuation. This is OK, because no such user exists - shmem + * is the only user that can pass nr > 1, and it never re-duplicates any swap + * entry it owns. */ -int swap_duplicate(swp_entry_t entry) +int swap_duplicate_nr(swp_entry_t entry, int nr) { int err = 0; - while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM) + while (!err && __swap_duplicate(entry, 1, nr) == -ENOMEM) err = add_swap_count_continuation(entry, GFP_ATOMIC); return err; } -- 2.51.2