From nobody Thu Sep 11 02:04:26 2025 Received: from mail-pf1-f171.google.com (mail-pf1-f171.google.com [209.85.210.171]) (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 42C2333CEBA for ; Wed, 10 Sep 2025 16:09:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.171 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757520578; cv=none; b=Vk/sXXYKV6eOXa9tp3aYYbRJ8mdGm9qJbc1xeW4ty1Y9HlZEMvfqtwgLlA24ND5uKrblX2l7Hh5AIXx7VTTG+xhkY66zYyb4iFNfGQp+n/XuAV4+HW7ROtilTTq6GpFWRnEh5QjWtIzvnVKtMMjHCoJpDj3Nh80zkQpx89Xlkpg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757520578; c=relaxed/simple; bh=wezNe+McLtBEyF9B2AQrUKduS6WWFRf6QeCr+ValA6A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NhbFysAauzJB8dLiDB+UVG4qFn6iiJBLf0/hjM9HrvVvlFtegmIyYI/GkxMOxRl3f8/XcRIHvtcfTcTLZlH28ovM5AOtftTXdf3gcBUqabdBvKllnlpyv8DNv3zshK3eZV6fwy166BMB2cdffEfEcPEndX44Uwvt96ruQcH+DMY= 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=NhqYjrI3; arc=none smtp.client-ip=209.85.210.171 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="NhqYjrI3" Received: by mail-pf1-f171.google.com with SMTP id d2e1a72fcca58-7724cacc32bso5634755b3a.0 for ; Wed, 10 Sep 2025 09:09:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1757520575; x=1758125375; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:reply-to:references :in-reply-to:message-id:date:subject:cc:to:from:from:to:cc:subject :date:message-id:reply-to; bh=TXr0Gr+eyBH1J2ZOC4B1nLxnwl36iHb/5ARHAVX+lWM=; b=NhqYjrI3efKGWa2VjQLoN+h/VLJxY/3ZfgJpmNryCHTSTw71gVVyCJkiMyBV9/cwUe 3EMigPg41ACLsKi5NYfuuIrKkC+mlnbACONb3///vCKVMn62oqppXlaX6ZDBJqODfOF4 A3W9VZV5wSDfOfzREQykNZGNWe27e2mQrIIh6smBYc1hGJ872VcGikX5veSU/3/lpaA5 wFFTCR5VhWbGhd6AhtWnIzBS5K5Ccpo/tg6CN4h4U1uQZePjtZJLhEHcuFXFhy8NLww/ 6nJkEP0gAgk5mn4m7R41VVtPx3Gd/N3RalP2r/fgyOSTAF0yruiweKEBRDdB76jZcfWZ VoxQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757520575; x=1758125375; h=content-transfer-encoding:mime-version:reply-to:references :in-reply-to:message-id:date:subject:cc:to:from:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=TXr0Gr+eyBH1J2ZOC4B1nLxnwl36iHb/5ARHAVX+lWM=; b=qtsREnUDL+8btQxvA7rfQMcDtnUCbXeLAyBlzRd/YnoWsR3JvBNyNAw0EjmShsNqlh bGSRhjYLKtXOHx42MTnCtLrh17op5gIMtj1/fD9WWxKgStBTjVaIGoEEi/YMz8RXk9Rr 1fyYg+wvB/z2aTyCaK1T7s4xyFwDd/Fuig8Wbh2q654fJH1ILVJ0ga7M7+g6YCuqbC9O oYknuLdICzjcdJKHBbcDCBgaenyuhbkcKIxGVZnbgW25mJ9yDHHxnDYbxJttX3ddF7/8 sCdVfP6O7cIb1UIA0j0X+afQgflFpTUrf3c+Og9J+YL8gHPg4xCK+F1DKs2SHbiWwA2S EDjA== X-Forwarded-Encrypted: i=1; AJvYcCWPYHCEbZbjZuLNyxPfp2fIwL/9pS4UENsRMfHzhC508apaWbDcQEQFUsZVFrqNnZA+AEpKaKe+TqgKN5E=@vger.kernel.org X-Gm-Message-State: AOJu0YyvoQEfHvq6pv9MuxOSI6OObZVhZCpGdQdMRJVFsLA22NHgtM7R k7pnGdV9VfQp7HxCuF1/NREuP8VuOGNnMvy9YPIPqhenE2F8+6f2Nt6B X-Gm-Gg: ASbGncv2uz4XINcxDNHaCNKT3hkzv6nDBZbGNlmPDpV7MNlzwZYPj3CGzoLtL03Eya9 Bw+N69Oy/QzPJNcqkkL4s+zpoeB9jcW2ZcpqKX0GVLEuXliSZKoW2maG2prjh/9dLpBm4kkuRp3 sBAvRGQ1QQYYDPKJfkaNvYaifQX1Nfo3GdvYqo3IcqdMmJpedm29UpdiAQbZ/7mfnVniRAv4Avj lw/nkvorRAPxmiXYx8pjUtk3T784ve191BBNxQbbNKtDp4mgBuxdf/F3G15Vk4rBD0Ch4BMALY6 dH6bRpouvSWYGSQW3IXA3jnNwS/pW+J/LS7pofMDNwPgsXggpN0YwHG/m3EZdDNhBgCUC6UKF0Z DLgG6ZC4IHnqFrjoJyWDT3e4PnvsjEhamCG9R0z7y+ifdMVAvB+JaB5b0Mw== X-Google-Smtp-Source: AGHT+IGd1fs3d/xLWFIH8x0QD2Wv+0XsIfWldgkL360dAU+YTjAIy2jV9nMZXESeItmlntKEcr6Daw== X-Received: by 2002:a05:6a20:3d19:b0:24d:301a:79b1 with SMTP id adf61e73a8af0-2533e94d169mr26623227637.15.1757520575417; Wed, 10 Sep 2025 09:09:35 -0700 (PDT) Received: from KASONG-MC4.tencent.com ([101.32.222.185]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b54998a1068sm1000142a12.31.2025.09.10.09.09.30 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 10 Sep 2025 09:09:34 -0700 (PDT) From: Kairui Song To: linux-mm@kvack.org Cc: Kairui Song , Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , Barry Song , Baoquan He , Nhat Pham , Kemeng Shi , Baolin Wang , Ying Huang , Johannes Weiner , David Hildenbrand , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org, Kairui Song Subject: [PATCH v3 10/15] mm, swap: wrap swap cache replacement with a helper Date: Thu, 11 Sep 2025 00:08:28 +0800 Message-ID: <20250910160833.3464-11-ryncsn@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250910160833.3464-1-ryncsn@gmail.com> References: <20250910160833.3464-1-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 There are currently three swap cache users that are trying to replace an existing folio with a new one: huge memory splitting, migration, and shmem replacement. What they are doing is quite similar. Introduce a common helper for this. In later commits, this can be easily switched to use the swap table by updating this helper. The newly added helper also makes the swap cache API better defined, and make debugging easier by adding a few more debug checks. Migration and shmem replace are meant to clone the folio, including content, swap entry value, and flags. And splitting will adjust each sub folio's swap entry according to order, which could be non-uniform in the future. So document it clearly that it's the caller's responsibility to set up the new folio's swap entries and flags before calling the helper. The helper will just follow the new folio's entry value. This also prepares for replacing high-order folios in the swap cache. Currently, only splitting to order 0 is allowed for swap cache folios. Using the new helper, we can handle high-order folio splitting better. Signed-off-by: Kairui Song Reviewed-by: Baolin Wang --- mm/huge_memory.c | 4 +--- mm/migrate.c | 11 +++-------- mm/shmem.c | 10 ++-------- mm/swap.h | 5 +++++ mm/swap_state.c | 33 +++++++++++++++++++++++++++++++++ 5 files changed, 44 insertions(+), 19 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 26cedfcd7418..4c66e358685b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3798,9 +3798,7 @@ static int __folio_split(struct folio *folio, unsigne= d int new_order, * NOTE: shmem in swap cache is not supported yet. */ if (swap_cache) { - __xa_store(&swap_cache->i_pages, - swap_cache_index(new_folio->swap), - new_folio, 0); + __swap_cache_replace_folio(folio, new_folio); continue; } =20 diff --git a/mm/migrate.c b/mm/migrate.c index 8e435a078fc3..c69cc13db692 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -566,7 +566,6 @@ static int __folio_migrate_mapping(struct address_space= *mapping, struct zone *oldzone, *newzone; int dirty; long nr =3D folio_nr_pages(folio); - long entries, i; =20 if (!mapping) { /* Take off deferred split queue while frozen and memcg set */ @@ -615,9 +614,6 @@ static int __folio_migrate_mapping(struct address_space= *mapping, if (folio_test_swapcache(folio)) { folio_set_swapcache(newfolio); newfolio->private =3D folio_get_private(folio); - entries =3D nr; - } else { - entries =3D 1; } =20 /* Move dirty while folio refs frozen and newfolio not yet exposed */ @@ -627,11 +623,10 @@ static int __folio_migrate_mapping(struct address_spa= ce *mapping, folio_set_dirty(newfolio); } =20 - /* Swap cache still stores N entries instead of a high-order entry */ - for (i =3D 0; i < entries; i++) { + if (folio_test_swapcache(folio)) + __swap_cache_replace_folio(folio, newfolio); + else xas_store(&xas, newfolio); - xas_next(&xas); - } =20 /* * Drop cache reference from old folio by unfreezing diff --git a/mm/shmem.c b/mm/shmem.c index 5f395fab489c..8930780325da 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2086,10 +2086,8 @@ static int shmem_replace_folio(struct folio **foliop= , gfp_t gfp, struct folio *new, *old =3D *foliop; swp_entry_t entry =3D old->swap; struct address_space *swap_mapping =3D swap_address_space(entry); - pgoff_t swap_index =3D swap_cache_index(entry); - XA_STATE(xas, &swap_mapping->i_pages, swap_index); int nr_pages =3D folio_nr_pages(old); - int error =3D 0, i; + int error =3D 0; =20 /* * We have arrived here because our zones are constrained, so don't @@ -2118,12 +2116,8 @@ static int shmem_replace_folio(struct folio **foliop= , gfp_t gfp, new->swap =3D entry; folio_set_swapcache(new); =20 - /* Swap cache still stores N entries instead of a high-order entry */ xa_lock_irq(&swap_mapping->i_pages); - for (i =3D 0; i < nr_pages; i++) { - WARN_ON_ONCE(xas_store(&xas, new)); - xas_next(&xas); - } + __swap_cache_replace_folio(old, new); xa_unlock_irq(&swap_mapping->i_pages); =20 mem_cgroup_replace_folio(old, new); diff --git a/mm/swap.h b/mm/swap.h index 6c4acb549bec..fe579c81c6c4 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -185,6 +185,7 @@ int swap_cache_add_folio(struct folio *folio, swp_entry= _t entry, void swap_cache_del_folio(struct folio *folio); void __swap_cache_del_folio(struct folio *folio, swp_entry_t entry, void *shadow); +void __swap_cache_replace_folio(struct folio *old, struct folio *new); void swap_cache_clear_shadow(int type, unsigned long begin, unsigned long end); =20 @@ -336,6 +337,10 @@ static inline void __swap_cache_del_folio(struct folio= *folio, swp_entry_t entry { } =20 +static inline void __swap_cache_replace_folio(struct folio *old, struct fo= lio *new) +{ +} + static inline unsigned int folio_swap_flags(struct folio *folio) { return 0; diff --git a/mm/swap_state.c b/mm/swap_state.c index f3a32a06a950..d1f5b8fa52fc 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -234,6 +234,39 @@ void swap_cache_del_folio(struct folio *folio) folio_ref_sub(folio, folio_nr_pages(folio)); } =20 +/** + * __swap_cache_replace_folio - Replace a folio in the swap cache. + * @old: The old folio to be replaced. + * @new: The new folio. + * + * Replace an existing folio in the swap cache with a new folio. The + * caller is responsible for setting up the new folio's flag and swap + * entries. Replacement will take the new folio's swap entry value as + * the starting offset to override all slots covered by the new folio. + * + * Context: Caller must ensure both folios are locked, also lock the + * swap address_space that holds the old folio to avoid races. + */ +void __swap_cache_replace_folio(struct folio *old, struct folio *new) +{ + swp_entry_t entry =3D new->swap; + unsigned long nr_pages =3D folio_nr_pages(new); + unsigned long offset =3D swap_cache_index(entry); + unsigned long end =3D offset + nr_pages; + + XA_STATE(xas, &swap_address_space(entry)->i_pages, offset); + + VM_WARN_ON_ONCE(!folio_test_swapcache(old) || !folio_test_swapcache(new)); + VM_WARN_ON_ONCE(!folio_test_locked(old) || !folio_test_locked(new)); + VM_WARN_ON_ONCE(!entry.val); + + /* Swap cache still stores N entries instead of a high-order entry */ + do { + WARN_ON_ONCE(xas_store(&xas, new) !=3D old); + xas_next(&xas); + } while (++offset < end); +} + /** * swap_cache_clear_shadow - Clears a set of shadows in the swap cache. * @type: Indicates the swap device. --=20 2.51.0