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 D5E1438E5DB; Wed, 25 Feb 2026 09:21:50 +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=1772011310; cv=none; b=Zc6g7VFcaXJ2Cxy7uv1BHhYKIKB85SRaOOGSwMhYBqLemvkohjUqwAWq+vdYyj2OYepDUZIGgJ2bUj+bLRE/J8Eg6OkRRS4q/V8ozCy/PGOb1CYXbcDxMzGssLWb8oCex/Ffge856tNBArm2fcDk1yo/MJ8b+v1w2ThzzYUlON0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772011310; c=relaxed/simple; bh=kx7pq8DDspnaKIfXROIyERaWB0WWO84KzMGW4mlWQSw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=P8yQe7dS2cjb7KsO4Z6sdu7uS4h6+sS/211Im8Ev1Wg7OWNnpFi0OIrzrnsmt4a+hNeQUDzUxQyFnK2Kp6kZwmJTVBDt70vzI4dKyjH1IljTmKvngvhl9bSUXCHytQDIJOvtvZiPK7btQ1zV7IP0KV2WqW/ieCU+c1+tpwyBKdE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V+Xm/LYt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="V+Xm/LYt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA4C1C116D0; Wed, 25 Feb 2026 09:21:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772011310; bh=kx7pq8DDspnaKIfXROIyERaWB0WWO84KzMGW4mlWQSw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=V+Xm/LYtmxMDUJ5A8US73eDHyRZSl8sIZdld/LxkspZPgqIE9oLO7fLvhnBXQQii3 UO6DqoseaIx9fToKO6WQRhPGlraKtDYDKqo1I1N5LawSkpWqfFmMaxer+E2ihHqmk7 SAzDu92PidPFo3qpJC1Lh24gvDfAW3bjONnKh3UAW6IfQ6rjHzqU0V4VqSfeH68cAD XjXZkL4TILHLvhOTzPZ7efIYtU1i2C5FueVPt5MPiWbiLj3cKu5ZNmZhv6x7M9u7VB qIlwKMcxK39yIWX0bky32qPHXgTiEMDkdPhuSUalRSfKIycxVq60oSBpm5xR+O3sNs G3bNy3ZjetlSw== Message-ID: Date: Wed, 25 Feb 2026 10:21:41 +0100 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 00/10] guest_memfd: Track amount of memory allocated on inode To: Ackerley Tng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, pbonzini@redhat.com, shuah@kernel.org, seanjc@google.com, shivankg@amd.com, rick.p.edgecombe@intel.com, yan.y.zhao@intel.com, rientjes@google.com, fvdl@google.com, jthoughton@google.com, vannapurve@google.com, pratyush@kernel.org, pasha.tatashin@soleen.com, kalyazin@amazon.com, tabba@google.com, michael.roth@amd.com References: <9ef9a0bd-4cff-4518-b7fb-e65c9b761a5a@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/25/26 08:31, Ackerley Tng wrote: > Ackerley Tng writes: > >> "David Hildenbrand (Arm)" writes: >> >>> >>> [...snip...] >>> >>> >>> If that avoids having to implement truncation completely ourselves, that might be one >>> option we could discuss, yes. >>> >>> Something like: >>> >>> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst >>> index 7c753148af88..94f8bb81f017 100644 >>> --- a/Documentation/filesystems/vfs.rst >>> +++ b/Documentation/filesystems/vfs.rst >>> @@ -764,6 +764,7 @@ cache in your filesystem. The following members are defined: >>> sector_t (*bmap)(struct address_space *, sector_t); >>> void (*invalidate_folio) (struct folio *, size_t start, size_t len); >>> bool (*release_folio)(struct folio *, gfp_t); >>> + void (*remove_folio)(struct folio *folio); >>> void (*free_folio)(struct folio *); >>> ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter); >>> int (*migrate_folio)(struct mapping *, struct folio *dst, >>> @@ -922,6 +923,11 @@ cache in your filesystem. The following members are defined: >>> its release_folio will need to ensure this. Possibly it can >>> clear the uptodate flag if it cannot free private data yet. >>> >>> +``remove_folio`` >>> + remove_folio is called just before the folio is removed from the >>> + page cache in order to allow the cleanup of properties (e.g., >>> + accounting) that needs the address_space mapping. >>> + >>> ``free_folio`` >>> free_folio is called once the folio is no longer visible in the >>> page cache in order to allow the cleanup of any private data. >>> diff --git a/include/linux/fs.h b/include/linux/fs.h >>> index 8b3dd145b25e..f7f6930977a1 100644 >>> --- a/include/linux/fs.h >>> +++ b/include/linux/fs.h >>> @@ -422,6 +422,7 @@ struct address_space_operations { >>> sector_t (*bmap)(struct address_space *, sector_t); >>> void (*invalidate_folio) (struct folio *, size_t offset, size_t len); >>> bool (*release_folio)(struct folio *, gfp_t); >>> + void (*remove_folio)(struct folio *folio); >>> void (*free_folio)(struct folio *folio); >>> ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter); >>> /* >>> diff --git a/mm/filemap.c b/mm/filemap.c >>> index 6cd7974d4ada..5a810eaacab2 100644 >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -250,8 +250,14 @@ void filemap_free_folio(struct address_space *mapping, struct folio *folio) >>> void filemap_remove_folio(struct folio *folio) >>> { >>> struct address_space *mapping = folio->mapping; >>> + void (*remove_folio)(struct folio *); >>> >>> BUG_ON(!folio_test_locked(folio)); >>> + >>> + remove_folio = mapping->a_ops->remove_folio; >>> + if (unlikely(remove_folio)) >>> + remove_folio(folio); >>> + >>> spin_lock(&mapping->host->i_lock); >>> xa_lock_irq(&mapping->i_pages); >>> __filemap_remove_folio(folio, NULL); >>> >> >> Thanks for this suggestion, I'll try this out and send another revision. >> >>> >>> Ideally we'd perform it under the lock just after clearing folio->mapping, but I guess that >>> might be more controversial. >>> > > I'm not sure which lock you were referring to, I hope it's not the > inode's i_lock? Why is calling the callback under lock frowned upon? I meant the two locks: mapping->host->i_lock and mapping->i_pages. I'd assume new callbacks that might result in holding these precious locks longer might be a problem for some people. Well, maybe, maybe not. I guess .free_folio() is called outside the lock because it's assumed to possibly do more expensive operations. -- Cheers, David