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From: Shakeel Butt To: Joanne Koong Cc: Miklos Szeredi , linux-fsdevel@vger.kernel.org, josef@toxicpanda.com, bernd.schubert@fastmail.fm, jefflexu@linux.alibaba.com, hannes@cmpxchg.org, linux-mm@kvack.org, kernel-team@meta.com Subject: Re: [PATCH v2 2/2] fuse: remove tmp folio for writebacks and internal rb tree Message-ID: <5wgtyqxkmxr5vrcfksgv4mrrgxmuqmu5z3glgasb6nxxw4metr@c56mvtzeph2x> References: <20241014182228.1941246-1-joannelkoong@gmail.com> <20241014182228.1941246-3-joannelkoong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: D4EBEC0013 X-Stat-Signature: wy84r7wjcpgqk1mogchkc5dr7xtdgexo X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1729284423-708603 X-HE-Meta: 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 sRR041wI EWYBK7p2B8bwUNLm+PhXCdzIZahkiqKfuphHiUktI2Oh8QLmfsupsFqG6srIhbsNI9wsqFrOf9Gt9yIyDzVhFzW/klpAAix8NvQnjzmbJ+sBehNxacBPRI/aa1shsiJejwOlKEvw4KQafGMyC6/3mheOrEktENwHBOyWGqA7KW2GJWMZnamuPWfvL9qDHo5A6R3Mf X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Oct 18, 2024 at 12:57:08PM GMT, Joanne Koong wrote: > On Thu, Oct 17, 2024 at 10:57 PM Shakeel Butt wrote: > > > > On Thu, Oct 17, 2024 at 06:30:08PM GMT, Joanne Koong wrote: > > > On Tue, Oct 15, 2024 at 3:01 AM Miklos Szeredi wrote: > > > > > > > > On Mon, 14 Oct 2024 at 20:23, Joanne Koong wrote: > > > > > > > > > This change sets AS_NO_WRITEBACK_RECLAIM on the inode mapping so that > > > > > FUSE folios are not reclaimed and waited on while in writeback, and > > > > > removes the temporary folio + extra copying and the internal rb tree. > > > > > > > > What about sync(2)? And page migration? > > > > > > > > Hopefully there are no other cases, but I think a careful review of > > > > places where generic code waits for writeback is needed before we can > > > > say for sure. > > > > > > The places where I see this potential deadlock still being possible are: > > > * page migration when handling a page fault: > > > In particular, this path: handle_mm_fault() -> > > > __handle_mm_fault() -> handle_pte_fault() -> do_numa_page() -> > > > migrate_misplaced_folio() -> migrate_pages() -> migrate_pages_sync() > > > -> migrate_pages_batch() -> migrate_folio_unmap() -> > > > folio_wait_writeback() > > > > So, this is numa fault and if fuse server is not mapping the fuse folios > > which it is serving, in its address space then this is not an issue. > > However hugepage allocation on page fault can cause compaction which > > might migrate unrelated fuse folios. So, fuse server doing compaction > > is an issue and we need to resolve similar to reclaim codepath. (Though > > I think for THP it is not doing MIGRATE_SYNC but doing for gigantic > > hugetlb pages). > > Thanks for the explanation. Would you mind pointing me to the > compaction function where this triggers the migrate? Is this in > compact_zone() where it calls migrate_pages() on the cc->migratepages > list? > Something like the following: __alloc_pages_direct_compact() -> try_to_compact_pages() -> compact_zone_order() -> /* MIGRATE_ASYNC or MIGRATE_SYNC_LIGHT */ compact_zone() -> migrate_pages() -> migrate_pages_sync() -> migrate_pages_batch() -> migrate_folio_unmap() -> folio_wait_writeback() The following is one code path from hugetlb: alloc_contig_range_noprof() -> /* MIGRATE_SYNC */ __alloc_contig_migrate_range() -> migrate_pages() -> migrate_pages_sync() -> migrate_pages_batch() -> migrate_folio_unmap() -> folio_wait_writeback()