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b=V+Xm/LYtmxMDUJ5A8US73eDHyRZSl8sIZdld/LxkspZPgqIE9oLO7fLvhnBXQQii3 UO6DqoseaIx9fToKO6WQRhPGlraKtDYDKqo1I1N5LawSkpWqfFmMaxer+E2ihHqmk7 SAzDu92PidPFo3qpJC1Lh24gvDfAW3bjONnKh3UAW6IfQ6rjHzqU0V4VqSfeH68cAD XjXZkL4TILHLvhOTzPZ7efIYtU1i2C5FueVPt5MPiWbiLj3cKu5ZNmZhv6x7M9u7VB qIlwKMcxK39yIWX0bky32qPHXgTiEMDkdPhuSUalRSfKIycxVq60oSBpm5xR+O3sNs G3bNy3ZjetlSw== Message-ID: Date: Wed, 25 Feb 2026 10:21:41 +0100 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 X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: C476740009 X-Stat-Signature: x7jydcne1acohj6uyoriaj66ycs6gtn9 X-HE-Tag: 1772011311-301448 X-HE-Meta: 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 DezWuoWD VYm6AoI+ic+mwVnfqNwR7nQN+/OF4GG6/WTwV5YbaFu5LEwKpTIUuVK9gMySzjroPrMJ59K+idCpiHBKwWx5rcFOdOLUnFI5x3y5VBjbbXh1MKdyiiltt83I+wQhBdh0GDsC1fXz9qKJmSqB6T/wWgKjH/2Y2KQXENUEKFL4GUkYfqNTMzlMcKQTDNt/mlwabhauouwrC2Nf3Rn40TVd2DTHFPRfgE8qcdJSOT5SUGcfKLamM2X632O1HPsmrrHXj79bMQ8ZXrF11Dn1NOdquqf834aA/2aLXe8Z3AnubW84pK1Bf+be1GYo9vEF4fvq7FyEHAeUKsM5qdTLdmt6IrAKk8XQ+bes+LkjH Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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