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Fri, 29 May 2026 09:47:07 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id HtzNEJtgGWqFZQAAD6G6ig (envelope-from ); Fri, 29 May 2026 09:47:07 +0000 Date: Fri, 29 May 2026 10:47:05 +0100 From: Pedro Falcato To: Usama Arif Cc: Andrew Morton , david@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org, r@hev.cc, jack@suse.cz, Andrew Donnellan , apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, brauner@kernel.org, catalin.marinas@arm.com, dev.jain@arm.com, kees@kernel.org, kevin.brodsky@arm.com, lance.yang@linux.dev, "Liam R. Howlett" , linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, npache@redhat.com, pasha.tatashin@soleen.com, rmclure@linux.ibm.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, Al Viro , wilts.infradead.org@pedro-suse.lan, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com Subject: Re: [PATCH v6 1/2] mm: bypass mmap_miss heuristic for VM_EXEC readahead Message-ID: References: <20260528165635.2068012-1-usama.arif@linux.dev> <20260528165635.2068012-2-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260528165635.2068012-2-usama.arif@linux.dev> X-Rspamd-Action: no action X-Stat-Signature: idi3x5d559cehijkcziw64ohtasrjfsf X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3FDE94000C X-HE-Tag: 1780048031-640370 X-HE-Meta: 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 xiZrN/cJ bsIziU3Pwra+HM6fmOWk/RCAoFfRw+H37xScegJl8kR9IMJRV+1MYNqG8SYPHNYoKqLBYxovCTLb8TcBhoBFsLrK6HH+U7v25v0uxBYllqqRL4/J+0nYk0jWOsckO+kqha8GNgEdYSeDHRZxelHjD+MpeNcAQDYFo6QQnzzLbBQ8ErEQ6iB5zHR9OMqN/K33trhGe9JTjYUdwNbD2cnP0nro1mLk6GfGW+tAwH+G8DUwyZmSgov2xK37/3JXPrtZF/mYYhgTXwqoiETtnmUFtHqZkCC8lPNzwS/lc6xeoRAhQ4rDysttmWCgyBQHAFuPM6Gtg8yIlAx9DRTjPhp3VLpiKg1YtzJmIXKvdx/Zw3tZFiKPNN2AcuYw/UvrAod8J8Bz8ttwdLG3f75npS3cHOWQMpfTrDT2isqKl+Ho4Yeh9n6lGDdS3oP6sYh7f48tR5Q6U Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, May 28, 2026 at 09:55:19AM -0700, Usama Arif wrote: > The mmap_miss heuristic is intended to stop speculative mmap readahead > when a file looks like a random-access workload. That does not fit the > VM_EXEC path very well. > > VM_EXEC readahead is already constrained differently from ordinary mmap > read-around: it is bounded by the VMA, uses exec_folio_order() to choose > an order useful for executable mappings, and sets async_size to 0 so it > does not create follow-on readahead. When VM_HUGEPAGE is also present, > the larger readahead is an explicit userspace opt-in. > > The mmap_miss counter is decremented from cache-hit paths in > do_async_mmap_readahead() and filemap_map_pages(). Those paths are not > always enough to balance the synchronous miss increments for executable > mappings. In particular, when fault-around is effectively disabled, such > as configurations where fault_around_pages is 1, filemap_map_pages() is > not reached from the fault path. The counter can then become a stale > throttle for VM_EXEC mappings and suppress the readahead behavior that > the executable-specific path is trying to provide. > > Skip both mmap_miss increments and decrements for VM_EXEC mappings, > matching the existing VM_SEQ_READ treatment and keeping the counter > accounting symmetric. > > Signed-off-by: Usama Arif > Reviewed-by: Jan Kara > Reviewed-by: Kiryl Shutsemau (Meta) Reviewed-by: Pedro Falcato This is reasonable, thanks. > --- > mm/filemap.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index cca20e350c95..a16b33e0fc71 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3339,7 +3339,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > } > } > > - if (!(vm_flags & VM_SEQ_READ)) { > + if (!(vm_flags & (VM_SEQ_READ | VM_EXEC))) { > /* Avoid banging the cache line if not needed */ > mmap_miss = READ_ONCE(ra->mmap_miss); > if (mmap_miss < MMAP_LOTSAMISS * 10) > @@ -3434,12 +3434,12 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf, > * times for a single folio and break the balance with mmap_miss > * increase in do_sync_mmap_readahead(). > * > - * VM_SEQ_READ mappings skip the mmap_miss increment in > + * VM_SEQ_READ and VM_EXEC mappings skip the mmap_miss increment in > * do_sync_mmap_readahead(), so skip the decrement here as well to > * keep the counter symmetric. > */ > if (likely(!folio_test_locked(folio)) && > - !(vmf->vma->vm_flags & VM_SEQ_READ)) { > + !(vmf->vma->vm_flags & (VM_SEQ_READ | VM_EXEC))) { > mmap_miss = READ_ONCE(ra->mmap_miss); > if (mmap_miss) > WRITE_ONCE(ra->mmap_miss, --mmap_miss); > @@ -3941,14 +3941,14 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > * Don't decrease mmap_miss in this scenario to make sure > * we can stop read-ahead. > * > - * VM_SEQ_READ mappings skip the mmap_miss increment in > - * do_sync_mmap_readahead(), so skip the decrement here as > - * well to keep the counter symmetric. > + * VM_SEQ_READ and VM_EXEC mappings skip the mmap_miss > + * increment in do_sync_mmap_readahead(), so skip the > + * decrement here as well to keep the counter symmetric. > */ > if ((map_ret & VM_FAULT_NOPAGE) && > !(vmf->flags & FAULT_FLAG_TRIED) && > !folio_test_workingset(folio) && > - !(vma->vm_flags & VM_SEQ_READ)) { > + !(vma->vm_flags & (VM_SEQ_READ | VM_EXEC))) { > unsigned short mmap_miss; > > mmap_miss = READ_ONCE(file->f_ra.mmap_miss); > -- > 2.52.0 > > -- Pedro