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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 , ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com Subject: Re: [PATCH v7 1/2] mm: bypass mmap_miss heuristic for VM_EXEC readahead Message-ID: References: <20260601102205.3985788-1-usama.arif@linux.dev> <20260601102205.3985788-2-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260601102205.3985788-2-usama.arif@linux.dev> X-Spamd-Result: default: False [-2.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[36]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RLxu57a9hfgn7tttf5jiwuqe5o)]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TAGGED_RCPT(0.00)[kernel]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[linux.dev:email,suse.cz:email,suse.de:email,imap1.dmz-prg2.suse.org:helo] X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260604_123055_278126_935A4B69 X-CRM114-Status: GOOD ( 30.32 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jun 01, 2026 at 03:21:17AM -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 > --- > 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))) { Just a side comment: I really hate these adhoc criteria all around filemap/readahead. One day we ought to actually write things down, and write things in a way that isn't entirely mysterious. I might see if I send a patch for this down the line... > /* 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