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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774015447; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OruWX6Y+VrnzFhcejZb+iVJL+JhqwtkaO5WVBgW6UjQ=; b=NrVkySz8XFBNwS4JdeWfeBofM4ytOBdZdZrAkUxNYCNGh3uxuRAPJ5YcoZEoeOwqFWU0CL f+YfK4i/Zn1/yHJ1X93vajWc3NlKybjlbIro8UCI06nC4kwGlmM9uk9uEpVJpjEETXdRI4 Pbjc2GicF57gusHNd3E8jN/ghaAy2VM= From: Usama Arif To: Andrew Morton , david@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org Cc: r@hev.cc, jack@suse.cz, ajd@linux.ibm.com, 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.Howlett@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, lorenzo.stoakes@oracle.com, 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@kvack.org, "linux-fsdevel@vger.kernel.l"@kernel.org, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com, Usama Arif Subject: [PATCH v2 1/4] mm: bypass mmap_miss heuristic for VM_EXEC readahead Date: Fri, 20 Mar 2026 06:58:51 -0700 Message-ID: <20260320140315.979307-2-usama.arif@linux.dev> In-Reply-To: <20260320140315.979307-1-usama.arif@linux.dev> References: <20260320140315.979307-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 38BAE14000F X-Stat-Signature: orbpkyu4qwnp8wphsic4py6smhkzpxcj X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1774015451-700267 X-HE-Meta: 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 7yceT+XV n0h6D2FWFk+ahEu4MABI98dL14t2Xyaun0lHAwKb8gGlGkcB3hnB5B5jPVpbTdQu3BO50BYIZiAmSxv2csjV6XZzYqKkaY/FF3wriEI2w71k5aHY7+JUqwUheFWc4Y986c3x8KgtF9AdaM0WUh5l3FKOTexZ+RfwiMJq3XTJqSvHpTJbeNKzZgZAstmLRoyqXnFaPnx/uymPG4QeKP8iHI4y/pkBMbahGo/2r8QT6n0lEUGSqdrN1AWOYDiUFNPXN60Z7wHLYZHcQw0uU4xnZYonClVjCaq4c7CJITXdh27KAIQ7m8p1UCA4IRPcSrd2/js0+nIosK+L7mx0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The mmap_miss counter in do_sync_mmap_readahead() tracks whether readahead is useful for mmap'd file access. It is incremented by 1 on every page cache miss in do_sync_mmap_readahead(), and decremented in two places: - filemap_map_pages(): decremented by N for each of N pages successfully mapped via fault-around (pages found already in cache, evidence readahead was useful). Only pages not in the workingset count as hits. - do_async_mmap_readahead(): decremented by 1 when a page with PG_readahead is found in cache. When the counter exceeds MMAP_LOTSAMISS (100), all readahead is disabled, including the targeted VM_EXEC readahead [1] that requests large folio orders for contpte mapping. On arm64 with 64K base pages, both decrement paths are inactive: 1. filemap_map_pages() is never called because fault_around_pages (65536 >> PAGE_SHIFT = 1) disables should_fault_around(), which requires fault_around_pages > 1. With only 1 page in the fault-around window, there is nothing "around" to map. 2. do_async_mmap_readahead() never fires for exec mappings because exec readahead sets async_size = 0, so no PG_readahead markers are placed. With no decrements, mmap_miss monotonically increases past MMAP_LOTSAMISS after 100 page faults, disabling all subsequent exec readahead. Fix this by excluding VM_EXEC VMAs from the mmap_miss logic, similar to how VM_SEQ_READ is already excluded. The exec readahead path is targeted (one folio at the fault location, async_size=0), not speculative prefetch, so the mmap_miss heuristic designed to throttle wasteful speculative readahead should not apply to it. [1] https://lore.kernel.org/all/20250430145920.3748738-6-ryan.roberts@arm.com/ Signed-off-by: Usama Arif --- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 6cd7974d4adab..7d89c6b384cc4 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3331,7 +3331,7 @@ 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) -- 2.52.0