From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0C7964A06 for ; Wed, 17 Sep 2025 01:06:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758071168; cv=none; b=rev/5Nf6r82t32xaYpRFwkVLmVuPg4SOaJfU/RxhXjBp6JLAkfvVAJVl6cqfF/PauGZMl0tZ48wMeslmpPS40ItpF0RxIAEkqBsRyUmGxrMDRHLz1hPD7eujyro+fkEpBQAciu0HpLucbr7qA1yx3onROzV2AdsvnA16hpasRxE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758071168; c=relaxed/simple; bh=tSyNqAZcWKRr3vhFtJ3JV+jgxDtST7M4f/yiOlZPlMo=; h=Date:To:From:Subject:Message-Id; b=JelIiPrnQg2Lc5rc2vHKrDfPBYMgH6SUoBnRBGRJVd6K186MkbNSKQQKUK+CChBWg3eAHuBvGxi4e6gRRr2f6UJGkWuZWe0zOSg2qcTd2RB18LPG5GDrO27VwrgljwqXvNvcX/GqjIw6fKOOzvVLPSrTwuR8lCV/OS0pIYaXVPo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=LgduB9kb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="LgduB9kb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6F22C4CEF9; Wed, 17 Sep 2025 01:06:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1758071167; bh=tSyNqAZcWKRr3vhFtJ3JV+jgxDtST7M4f/yiOlZPlMo=; h=Date:To:From:Subject:From; b=LgduB9kb4MgjgZrgCAACEbdbnniFhuN02n96adaw2IbB4xZlt/jEvbqCwSy6qjDVk PhLAutYz3D0zx4Xbc5Met1r2yTl64dZEQmzvFOjI8TSzgUfQ+ENl1uXr7syGVZ6CA5 2fcT0FIOEgnGSX4AKha5d0sOeFxj+/+5BuPO7Dt4= Date: Tue, 16 Sep 2025 18:06:07 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,yosryahmed@google.com,ying.huang@linux.alibaba.com,willy@infradead.org,shikemeng@huaweicloud.com,oliver.sang@intel.com,nphamcs@gmail.com,lorenzo.stoakes@oracle.com,hughd@google.com,hannes@cmpxchg.org,david@redhat.com,chrisl@kernel.org,bhe@redhat.com,baolin.wang@linux.alibaba.com,baohua@kernel.org,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-swap-wrap-swap-cache-replacement-with-a-helper.patch added to mm-unstable branch Message-Id: <20250917010607.D6F22C4CEF9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm, swap: wrap swap cache replacement with a helper has been added to the -mm mm-unstable branch. Its filename is mm-swap-wrap-swap-cache-replacement-with-a-helper.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-wrap-swap-cache-replacement-with-a-helper.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Kairui Song Subject: mm, swap: wrap swap cache replacement with a helper Date: Wed, 17 Sep 2025 00:00:55 +0800 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. Link: https://lkml.kernel.org/r/20250916160100.31545-11-ryncsn@gmail.com Signed-off-by: Kairui Song Reviewed-by: Baolin Wang Acked-by: David Hildenbrand Acked-by: Chris Li Suggested-by: Chris Li Cc: Baoquan He Cc: Barry Song Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Johannes Weiner Cc: Kemeng Shi Cc: kernel test robot Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Nhat Pham Cc: Yosry Ahmed Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/huge_memory.c | 4 +--- mm/migrate.c | 11 +++-------- mm/shmem.c | 11 ++--------- mm/swap.h | 5 +++++ mm/swap_state.c | 33 +++++++++++++++++++++++++++++++++ 5 files changed, 44 insertions(+), 20 deletions(-) --- a/mm/huge_memory.c~mm-swap-wrap-swap-cache-replacement-with-a-helper +++ a/mm/huge_memory.c @@ -3798,9 +3798,7 @@ static int __folio_split(struct folio *f * 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; } --- a/mm/migrate.c~mm-swap-wrap-swap-cache-replacement-with-a-helper +++ a/mm/migrate.c @@ -566,7 +566,6 @@ static int __folio_migrate_mapping(struc struct zone *oldzone, *newzone; int dirty; long nr = folio_nr_pages(folio); - long entries, i; if (!mapping) { /* Take off deferred split queue while frozen and memcg set */ @@ -615,9 +614,6 @@ static int __folio_migrate_mapping(struc if (folio_test_swapcache(folio)) { folio_set_swapcache(newfolio); newfolio->private = folio_get_private(folio); - entries = nr; - } else { - entries = 1; } /* Move dirty while folio refs frozen and newfolio not yet exposed */ @@ -627,11 +623,10 @@ static int __folio_migrate_mapping(struc folio_set_dirty(newfolio); } - /* Swap cache still stores N entries instead of a high-order entry */ - for (i = 0; i < entries; i++) { + if (folio_test_swapcache(folio)) + __swap_cache_replace_folio(folio, newfolio); + else xas_store(&xas, newfolio); - xas_next(&xas); - } /* * Drop cache reference from old folio by unfreezing --- a/mm/shmem.c~mm-swap-wrap-swap-cache-replacement-with-a-helper +++ a/mm/shmem.c @@ -2086,10 +2086,8 @@ static int shmem_replace_folio(struct fo struct folio *new, *old = *foliop; swp_entry_t entry = old->swap; struct address_space *swap_mapping = swap_address_space(entry); - pgoff_t swap_index = swap_cache_index(entry); - XA_STATE(xas, &swap_mapping->i_pages, swap_index); int nr_pages = folio_nr_pages(old); - int error = 0, i; + int error = 0; /* * We have arrived here because our zones are constrained, so don't @@ -2118,13 +2116,8 @@ static int shmem_replace_folio(struct fo new->swap = entry; folio_set_swapcache(new); - /* Swap cache still stores N entries instead of a high-order entry */ xa_lock_irq(&swap_mapping->i_pages); - for (i = 0; i < nr_pages; i++) { - WARN_ON_ONCE(xas_store(&xas, new) != old); - xas_next(&xas); - } - + __swap_cache_replace_folio(old, new); mem_cgroup_replace_folio(old, new); shmem_update_stats(new, nr_pages); shmem_update_stats(old, -nr_pages); --- a/mm/swap.h~mm-swap-wrap-swap-cache-replacement-with-a-helper +++ a/mm/swap.h @@ -185,6 +185,7 @@ int swap_cache_add_folio(struct folio *f 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); @@ -336,6 +337,10 @@ static inline void __swap_cache_del_foli { } +static inline void __swap_cache_replace_folio(struct folio *old, struct folio *new) +{ +} + static inline unsigned int folio_swap_flags(struct folio *folio) { return 0; --- a/mm/swap_state.c~mm-swap-wrap-swap-cache-replacement-with-a-helper +++ a/mm/swap_state.c @@ -235,6 +235,39 @@ void swap_cache_del_folio(struct folio * } /** + * __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 = new->swap; + unsigned long nr_pages = folio_nr_pages(new); + unsigned long offset = swap_cache_index(entry); + unsigned long end = 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) != 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. * @begin: Beginning offset of the range. _ Patches currently in -mm which might be from kasong@tencent.com are mm-swap-use-unified-helper-for-swap-cache-look-up.patch mm-swap-fix-swap-cache-index-error-when-retrying-reclaim.patch mm-swap-check-page-poison-flag-after-locking-it.patch mm-swap-always-lock-and-check-the-swap-cache-folio-before-use.patch mm-swap-rename-and-move-some-swap-cluster-definition-and-helpers.patch mm-swap-tidy-up-swap-device-and-cluster-info-helpers.patch mm-swap-cleanup-swap-cache-api-and-add-kerneldoc.patch mm-shmem-swap-remove-redundant-error-handling-for-replacing-folio.patch mm-swap-wrap-swap-cache-replacement-with-a-helper.patch mm-swap-use-the-swap-table-for-the-swap-cache-and-switch-api.patch mm-swap-mark-swap-address-space-ro-and-add-context-debug-check.patch mm-swap-remove-contention-workaround-for-swap-cache.patch mm-swap-implement-dynamic-allocation-of-swap-table.patch mm-swap-use-a-single-page-for-swap-table-when-the-size-fits.patch