From: "Oscar Salvador (SUSE)" <osalvador@kernel•org>
To: Usama Arif <usama.arif@linux•dev>
Cc: Andrew Morton <akpm@linux-foundation•org>,
david@kernel•org, willy@infradead•org, ryan.roberts@arm•com,
linux-mm@kvack•org, pfalcato@suse•de, r@hev•cc, jack@suse•cz,
Andrew Donnellan <andrew+kernel@donnellan•id.au>,
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" <liam@infradead•org>,
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 <viro@zeniv•linux.org.uk>,
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
Date: Tue, 2 Jun 2026 05:51:03 +0200 [thread overview]
Message-ID: <ah5TJ8tNqcztGS4F@localhost.localdomain> (raw)
In-Reply-To: <20260601102205.3985788-2-usama.arif@linux.dev>
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 <usama.arif@linux•dev>
> Reviewed-by: Jan Kara <jack@suse•cz>
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel•org>
Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel•org>
--
Oscar Salvador
SUSE Labs
next prev parent reply other threads:[~2026-06-02 3:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-01 10:21 [PATCH v7 0/2] mm: improve large folio readahead for exec memory Usama Arif
2026-06-01 10:21 ` [PATCH v7 1/2] mm: bypass mmap_miss heuristic for VM_EXEC readahead Usama Arif
2026-06-02 3:51 ` Oscar Salvador (SUSE) [this message]
2026-06-04 19:30 ` Pedro Falcato
2026-06-01 10:21 ` [PATCH v7 2/2] mm: use mapping_max_folio_order() for force_thp_readahead order Usama Arif
2026-06-01 16:22 ` Jan Kara
2026-06-04 19:33 ` Pedro Falcato
2026-06-01 23:10 ` [PATCH v7 0/2] mm: improve large folio readahead for exec memory Andrew Morton
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