From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta0.migadu.com (out-186.mta0.migadu.com [91.218.175.186]) (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 746D23D7D74 for ; Tue, 7 Jul 2026 10:08:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783418925; cv=none; b=VkBcQxq2TNlSBVnwCCxAEa2K0A2qZpZ9Ad9yeCx2ffos8xC4S8JAC+9J1fStXXLK8nsxwr2EFV6y21JD48rguw9e4ECRJ8qLfltSAnbgsD/jn6vWl/qt5YTvoDYwj8pl3N2KKimDXde1B1oB64eAI5bmr2cNwWi7MsPK3S2f5l0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783418925; c=relaxed/simple; bh=Pl+xTdXlBj53V35OTq24lXUNw6g6tnkPUU7CelWHmcE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tnL1JzBtG3fKjfY1yVqI00coiKSf5z2NhQATFbWGktj+ZBhzydg23jU7CCaEIfh900dLLQyppUYSt0ZNvMfbuO2Cu68BQ7/itw9Fr5Aj2A6Oe6S5PVgn+BPaXsJoBSMcjtBw2jUJ/AAEImi/WYmcFqvNpa/oncl8dPOCBg5eu7w= 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=lJA3uk1u; arc=none smtp.client-ip=91.218.175.186 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="lJA3uk1u" Message-ID: <5d423660-dae1-4ab9-a656-7e488cf98321@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783418919; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TUY55oS394CtAuTTigq+2eRfUqPG18NKirH243JNBP0=; b=lJA3uk1ukFUMfWyOdmT6NDSS6hxI2mmC8DrlSshGOnPVKLBhJRCY+4xQgy128Vr/Y2mtjI Vpg1W6uVYZQs9rrq2fdwT1N/rrhYR1MU1u3Q8iOWa3zaztOREs5vZdtIhOlgz8/+tYiIA+ Y2npszhgSvrVEVA7tVaetbbllI63P2w= Date: Tue, 7 Jul 2026 11:08:36 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 04/11] mm: zswap: add range lookup for large-folio swapin To: Yosry Ahmed Cc: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, 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, npache@redhat.com, "Liam R. Howlett" , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, kernel-team@meta.com, Alexandre Ghiti References: <20260703173903.3789516-1-usama.arif@linux.dev> <20260703173903.3789516-5-usama.arif@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 06/07/2026 22:36, Yosry Ahmed wrote: > On Fri, Jul 03, 2026 at 10:38:21AM -0700, Usama Arif wrote: >> 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. >> >> Add zswap_range_has_entry() so PMD swap-entry consumers can make the >> same range decision before attempting PMD-order swapin. >> >> Signed-off-by: Alexandre Ghiti >> Signed-off-by: Usama Arif > > I found this by accident, please CC me on zswap changes :) > Sorry about this! I will CC you in all future revisions of this series. >> --- >> include/linux/zswap.h | 7 +++++++ >> mm/zswap.c | 46 +++++++++++++++++++++++++++++++++---------- >> 2 files changed, 43 insertions(+), 10 deletions(-) >> >> diff --git a/include/linux/zswap.h b/include/linux/zswap.h >> index 30c193a1207e..de10aa528597 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_range_has_entry(swp_entry_t entry, unsigned int nr); >> #else >> >> struct zswap_lruvec_state {}; >> @@ -69,6 +70,12 @@ static inline bool zswap_never_enabled(void) >> return true; >> } >> >> +static inline bool zswap_range_has_entry(swp_entry_t entry, >> + unsigned int nr) >> +{ >> + return false; >> +} >> + >> #endif >> >> #endif /* _LINUX_ZSWAP_H */ >> diff --git a/mm/zswap.c b/mm/zswap.c >> index b5a17ea20237..89dd88a5223f 100644 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -1559,6 +1559,27 @@ bool zswap_store(struct folio *folio) >> return ret; >> } >> >> +/** >> + * zswap_range_has_entry() - is any slot in [entry, entry + nr) in zswap? >> + * @entry: base swap entry of the range >> + * @nr: number of contiguous slots to check >> + */ > > Maybe zswap_is_present() as suggested here: > https://lore.kernel.org/linux-mm/CAO9r8zNni28A+9BiDgDTBRuvGTKnqH91kpbpjjeftfnKSeSOJg@mail.gmail.com/. > > IIUC this interface can be used for the same purpose, we just need to > pass nr=1. Yes, this sounds better, will change in next revision. > >> +bool zswap_range_has_entry(swp_entry_t entry, unsigned int nr) >> +{ >> + pgoff_t offset = swp_offset(entry); >> + XA_STATE(xas, swap_zswap_tree(entry), offset); >> + bool found; >> + >> + if (!nr || zswap_never_enabled()) >> + return false; >> + >> + rcu_read_lock(); >> + found = !!xas_find(&xas, offset + nr - 1); >> + rcu_read_unlock(); > > Why not xa_find()? It seems to handle RCU locking as well as retrying. > Ack, will change in next revision, Thanks! >> + >> + return found; >> +} >> + >> /** >> * zswap_load() - load a folio from zswap >> * @folio: folio to load >> @@ -1571,10 +1592,9 @@ bool zswap_store(struct folio *folio) >> * 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, >> - * but NOT marked up-to-date, so that an IO error is emitted (e.g. >> - * do_swap_page() will SIGBUS). >> + * -EIO: if 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). >> * >> * -ENOENT: if the swapped out content was not in zswap. The folio remains >> * locked on return. >> @@ -1593,13 +1613,19 @@ 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 (zswap_range_has_entry(swp, folio_nr_pages(folio))) { >> + folio_unlock(folio); >> + return -EIO; >> + } >> + return -ENOENT; >> } >> >> entry = xa_load(tree, offset); >> -- >> 2.53.0-Meta >> >>