From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (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 0FF2F28850E for ; Tue, 18 Aug 2026 13:12:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058754; cv=none; b=Z+5LSGMBdPAwUb2XerLGbGOofSuzkn0ojiWcvpNn808yyePQAkykMFMS82LzjmMw28447a5jVGR0ZzT27HBmEcOApWSFzxmVo7zIc5CgfbpBxneTVNmVts0WtZhrFWPu2q3ZWqqwIweOfDUZzlOA/SdhgSGIuHX5JDDVSACK284= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058754; c=relaxed/simple; bh=FPWpaNmTRU+xlShU64gQ7An1URF32LkC2T1D7RJM8B8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Jh9uGAjH6nK4cVMYfIeiWAK231jtco3Sq2s4lKFo9hgx+wZSTiy3AC/pAjiPnokta0wTpH0kL4P4bzvbXXUzCSvtmZ8oSgp/jEXBvtUkc5C3poZpiOLfKWAQ3F5dNeR38wIbyacQqOZWxkVgKecP4KFfXWM/CeW9PO+r6U/mcWc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=fea0Iqtr; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="fea0Iqtr" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=FPWpaNmTRU+xlShU64gQ7An1URF32LkC2T1D7RJM8B8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787058751; v=1; x=1787663551; b=fea0IqtrG9VfdW11Ia+oI7Ez+E9ZswSNW2EYTFMalLV10nXvOUsWkhe47GUGBpIjpR1bQRac /rz211dnpHetCJsAXDxxbkV89Wo+Vp5FPwMfIcczEO4oDcFktLRA4g8J/b10Ynn6NZb4bg3koob OnWCfJSN9goBD4Dec+hZeV+I= X-Envelope-To: linux-kernel@vger.kernel.org Received: from localhost (2a03:2880:10ff:1a::) by mta12.migadu.com with ESMTPS id 7c31fdcbe05a5cd5; Tue, 18 Aug 2026 13:12:30 +0000 X-Migadu-Flow: FLOW_OUT From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, Nico Pache , Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, kernel-team@meta.com, Alexandre Ghiti , Usama Arif Subject: [PATCH v6 05/12] mm: zswap: add range lookup for large-folio swapin Date: Tue, 18 Aug 2026 06:09:46 -0700 Message-ID: <20260818131202.494754-6-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260818131202.494754-1-usama.arif@linux.dev> References: <20260818131202.494754-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alexandre Ghiti A large folio reaches zswap_load() only when the caller expects the whole range to be on disk. Zswap still stores large folios as independent order-0 entries, so reconstructing a large folio from zswap entries would risk returning partially initialized data. Teach zswap_load() to scan the covered range. If no slot is in zswap, return -ENOENT so swap_read_folio() reads the backing device. If any slot is still in zswap, fail the large-folio read so the caller can fall back to per-page swapin. Return -EIO rather than -EINVAL for that conflict. Large-folio loads are now valid requests; the error means zswap cannot safely satisfy the request from partial per-page compressed state, not that the request is unsupported. Existing callers only distinguish -ENOENT, so this is a semantic clarification rather than a behavioral change. Add zswap_is_present() so PMD swap-entry consumers can make the same range decision before attempting PMD-order swapin. Also use it from __swap_cache_add_check() for multi-page insertions while holding the swap cluster lock. That check runs before folio allocation and again immediately before swap-cache insertion, closing the race with zswap writeback and rejecting mixed zswap/disk backing with -EBUSY. Signed-off-by: Alexandre Ghiti Signed-off-by: Usama Arif --- include/linux/zswap.h | 6 ++++++ mm/swap_state.c | 10 ++++++++++ mm/zswap.c | 46 +++++++++++++++++++++++++++++++------------ 3 files changed, 49 insertions(+), 13 deletions(-) diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 30c193a1207e1..cd9efcf9dec94 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -35,6 +35,7 @@ void zswap_lruvec_state_init(struct lruvec *lruvec); void zswap_folio_swapin(struct folio *folio); bool zswap_is_enabled(void); bool zswap_never_enabled(void); +bool zswap_is_present(swp_entry_t entry, unsigned int nr); #else struct zswap_lruvec_state {}; @@ -69,6 +70,11 @@ static inline bool zswap_never_enabled(void) return true; } +static inline bool zswap_is_present(swp_entry_t entry, unsigned int nr) +{ + return false; +} + #endif #endif /* _LINUX_ZSWAP_H */ diff --git a/mm/swap_state.c b/mm/swap_state.c index b76eb3d876fd7..15e200d6966b9 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -191,6 +192,15 @@ static int __swap_cache_add_check(struct swap_cluster_info *ci, if (nr == 1) return 0; + /* + * The cluster lock serializes swap-cache insertion with zswap + * writeback. Reject mixed zswap/disk backing before allocating a + * large folio and recheck it before adding the folio to swap cache. + */ + if (zswap_is_present(swp_entry(swp_type(targ_entry), + round_down(swp_offset(targ_entry), nr)), nr)) + return -EBUSY; + is_zero = __swap_table_test_zero(ci, ci_off); ci_off = round_down(ci_off, nr); ci_end = ci_off + nr; diff --git a/mm/zswap.c b/mm/zswap.c index 37f34e406c8e3..32671dc2bf84d 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1571,6 +1571,23 @@ bool zswap_store(struct folio *folio) return ret; } +/** + * zswap_is_present() - is any slot in [entry, entry + nr) in zswap? + * @entry: base swap entry of the range + * @nr: number of contiguous slots to check (pass 1 for a single-slot query) + */ +bool zswap_is_present(swp_entry_t entry, unsigned int nr) +{ + pgoff_t offset = swp_offset(entry); + struct xarray *tree = swap_zswap_tree(entry); + unsigned long index = offset; + + if (!nr || zswap_never_enabled()) + return false; + + return xa_find(tree, &index, offset + nr - 1, XA_PRESENT); +} + /** * zswap_load() - load a folio from zswap * @folio: folio to load @@ -1578,13 +1595,9 @@ bool zswap_store(struct folio *folio) * Return: 0 on success, with the folio unlocked and marked up-to-date, or one * of the following error codes: * - * -EIO: if the swapped out content was in zswap, but could not be loaded - * into the page due to a decompression failure. The folio is unlocked, but - * NOT marked up-to-date, so that an IO error is emitted (e.g. do_swap_page() - * will SIGBUS). - * - * -EINVAL: if the swapped out content was in zswap, but the page belongs - * to a large folio, which is not supported by zswap. The folio is unlocked, + * -EIO: if the swapped out content was in zswap but could not be handed + * back, either because decompression failed or because a slot in a + * large-folio range is unexpectedly still in zswap. The folio is unlocked, * but NOT marked up-to-date, so that an IO error is emitted (e.g. * do_swap_page() will SIGBUS). * @@ -1605,13 +1618,20 @@ int zswap_load(struct folio *folio) return -ENOENT; /* - * Large folios should not be swapped in while zswap is being used, as - * they are not properly handled. Zswap does not properly load large - * folios, and a large folio may only be partially in zswap. + * A large folio reaches zswap_load() only when its whole range is + * expected to be on disk: PMD swap-entry consumers split before + * calling into PMD-order swapin whenever any slot is still in zswap. + * Confirm the range is entirely absent from zswap and return -ENOENT + * so the caller reads it from disk; if a slot is unexpectedly still in + * zswap, fail the read rather than return partially-initialized data. */ - if (WARN_ON_ONCE(folio_test_large(folio))) { - folio_unlock(folio); - return -EINVAL; + if (folio_test_large(folio)) { + if (WARN_ON_ONCE(zswap_is_present(swp, + folio_nr_pages(folio)))) { + folio_unlock(folio); + return -EIO; + } + return -ENOENT; } entry = xa_load(tree, offset); -- 2.53.0-Meta