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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775153624; 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=BYo+MsU3NDEL+koHfyTJu1xHHS5mV0CFXLaMn8ZezZo=; b=jBVlATxqIYgZfj3KHFj3T3aVBW1J8ZhMacXVtFHk4eHh5FwgyqeygxWtikdiA+B1T7VuFg v/zAHoBUYT/h+us80bWmoIGHjJz8uEo/Um3mzOQJ7+5N9tE4RDgdtwmMVvyXBJ/TJ40i0J 828uNtru0sPYXV9jPylnQLnOE7M8Y8c= 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 , 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, leitao@debian.org, kernel-team@meta.com, Usama Arif Subject: [PATCH v3 1/4] mm: bypass mmap_miss heuristic for VM_EXEC readahead Date: Thu, 2 Apr 2026 11:08:22 -0700 Message-ID: <20260402181326.3107102-2-usama.arif@linux.dev> In-Reply-To: <20260402181326.3107102-1-usama.arif@linux.dev> References: <20260402181326.3107102-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 1C3658000A X-Stat-Signature: 45ykxm1yciypt97jxpgckonkmoj3eexn X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1775153626-248830 X-HE-Meta: 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 HVGoZRke AaEi6y9QYZhhlxDnAxweCmxv2t4R5PryhJ5I7euqcunip9L3Z1fTkkKE0JB7/q2Er/WID7eEQYQQkmDjosVyigcgnO8ZrcV+0n7l7K0iCch6oUhNOSCScUIfMgaRT2S0K8W6UXljc93x8g144QhDuSqz2LfrsHja6hIidrtxp5wxSHQmpi3PYXlvq3u0fBnAzXiHuwDox8s5E8ynYltDhvFlxfsc9nJ/yHB42loptot5Ge6yPlC9z8L2/lHoRGCadw2jdUQ6sIvKkPQy2COVdzr2HmNtPVRJyZwbhpAxH+lQn0H0fh9XQO6lyet/NMgiUeov93u61KJtwR54= 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 Reviewed-by: Jan Kara Reviewed-by: Kiryl Shutsemau (Meta) --- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 2b933a1da9bd..a4ea869b2ca1 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3337,7 +3337,7 @@ 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