From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD48B175A77 for ; Fri, 20 Mar 2026 14:03:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774015440; cv=none; b=Tsa61+g94yLW5EYxVFrUuY3ycf+fvRkQWlHmW3KHdAOTqzsV6dlwtcSPd6n8HjKAuU9ZoleauLFv6SCvoyEC+Wz94F8SchG1ZRIKDDOfQ8ow6YV8cD1MpJKTJJuGXtZ+HVhWNym2uA16FVulAyMl5fqEOCIcXtU1g8JoSxnCMzI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774015440; c=relaxed/simple; bh=WIsru2BiyzE7Dk092bjfIfjlXQwISEJbpd6Ivo/EHFE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=VymY5S795Qp8wFJWcpmO/Gnx4QdV1arv3XV8aSHeZjhyAUBrLcYoSUBPuEJkwxAEkYdRgr0ky6j8Cu0GlhOKAFucr/bbsdHznTXIzTw+e5w1oUvyobfQrUUcNs9pN/n4w/5dw0A2e5UXM6ubxdqnYzFmPlKZlB4mo5GHoosfkSU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Tc4H5TGa; arc=none smtp.client-ip=95.215.58.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Tc4H5TGa" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774015435; 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; bh=BQlel+6dtoxswtHUU01IUBagcMsTT/u/Ie50MY6ZLbc=; b=Tc4H5TGa1InXyh4vPLhjJgYqKP6CKEGnb/v313Fr+gMkn4PrAhCfqSk/TZIoe+QcU9WTn2 nrnO3Z9ZeOl/Dm/qu+yr2Z4iUAddehyYbEyD7oWGABzmY5Vx7nrCBh8oH3aEiIdBlYPp40 IDhxBJfN4f4fFBp051wzopRpOn54ocA= 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, 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 0/4] mm: improve large folio readahead and alignment for exec memory Date: Fri, 20 Mar 2026 06:58:50 -0700 Message-ID: <20260320140315.979307-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT v2 takes a different approach from v1 trying to move away from exec_folio_order() and comeup with a generic arch independent solution which is what I think David was suggesting in [1]. I thought I would send it as code rather than try and discuss it in v1 as its easier :) v1 -> v2: https://lore.kernel.org/all/20260310145406.3073394-1-usama.arif@linux.dev/ - disable mmap_miss logic for VM_EXEC (Jan Kara) - Align in elf only when segment VA and file offset are already aligned (Rui) - preferred_exec_order() for VM_EXEC sync mmap_readahead which takes into account zone high watermarks (as an approximation of memory pressure) (David, or atleast my approach to what David suggested in [1] :)) - Extend max alignment to mapping_max_folio_size() instead of exec_folio_order() Motiviation =========== exec_folio_order() was introduced [2] to request readahead at an arch-preferred folio order for executable memory, enabling hardware PTE coalescing (e.g. arm64 contpte) and PMD mappings on the fault path. However, several things prevent this from working optimally: 1. The mmap_miss heuristic in do_sync_mmap_readahead() silently disables exec readahead after 100 page faults. The mmap_miss counter tracks whether readahead is useful for mmap'd file access: - Incremented by 1 in do_sync_mmap_readahead() on every page cache miss (page needed IO). - Decremented by N in filemap_map_pages() for N pages successfully mapped via fault-around (pages found in cache without faulting, evidence that readahead was useful). Only non-workingset pages count and recently evicted and re-read pages don't count as hits. - Decremented by 1 in do_async_mmap_readahead() when a PG_readahead marker page is found (indicates sequential consumption of readahead pages). When mmap_miss exceeds MMAP_LOTSAMISS (100), all readahead is disabled. On arm64 with 64K pages, both decrement paths are inactive: - 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. - 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 faults, disabling exec readahead for the remainder of the mapping. Patch 1 fixes this by excluding VM_EXEC VMAs from the mmap_miss logic, similar to how VM_SEQ_READ is already excluded. 2. exec_folio_order() is an arch-specific hook that returns a static order (ilog2(SZ_64K >> PAGE_SHIFT)), which is suboptimal for non-4K page sizes and doesn't adapt to runtime conditions. Patch 2 replaces it with a generic preferred_exec_order() that targets min(PMD_ORDER, 2M), which naturally gives the right answer across architectures and different page sizes: contpte on arm64 (2M for all page sizes), PMD mapping on x86 (2M), and smaller PMDs like s390 (1M). The 2M cap also avoids requesting excessively large folios on configurations where PMD_ORDER is much larger (32M on arm64 16K pages, 512M on arm64 64K pages), which would cause unnecessary memory pressure. The function adapts at runtime based on VMA size and memory pressure (zone watermarks), stepping down the order when memory is tight. 3. Even with correct folio order and readahead, hardware PTE coalescing (e.g. contpte) and PMD mapping require the virtual address to be aligned to the folio size. The readahead path aligns file offsets and the buddy allocator aligns physical memory, but the virtual address depends on the VMA start. For PIE binaries, ASLR randomizes the load address at PAGE_SIZE granularity, so on arm64 with 64K pages only 1/32 of load addresses are 2M-aligned. When misaligned, contpte cannot be used for any folio in the VMA. Patch 3 fixes this for the main binary by extending maximum_alignment() in the ELF loader to consider mapping_max_folio_size(), aligning load_bias to the largest folio the filesystem will allocate. Patch 4 fixes this for shared libraries by adding a folio-size alignment fallback in thp_get_unmapped_area_vmflags(). The existing PMD_SIZE alignment (512M on arm64 64K pages) is too large for typical shared libraries, so this smaller fallback succeeds where PMD fails. I created a benchmark that mmaps a large executable file and calls RET-stub functions at PAGE_SIZE offsets across it. "Cold" measures fault + readahead cost. "Random" first faults in all pages with a sequential sweep (not measured), then measures time for calling random offsets, isolating iTLB miss cost for scattered execution. The benchmark results on Neoverse V2 (Grace), arm64 with 64K base pages, 512MB executable file on ext4, averaged over 3 runs: Phase | Baseline | Patched | Improvement -----------|--------------|--------------|------------------ Cold fault | 83.4 ms | 41.3 ms | 50% faster Random | 76.0 ms | 58.3 ms | 23% faster [1] https://lore.kernel.org/all/d72d5ca3-4b92-470e-9f89-9f39a3975f1e@kernel.org/ [2] https://lore.kernel.org/all/20250430145920.3748738-6-ryan.roberts@arm.com/ Usama Arif (4): mm: bypass mmap_miss heuristic for VM_EXEC readahead mm: replace exec_folio_order() with generic preferred_exec_order() elf: align ET_DYN base to max folio size for PTE coalescing mm: align file-backed mmap to max folio order in thp_get_unmapped_area arch/arm64/include/asm/pgtable.h | 8 ----- fs/binfmt_elf.c | 38 ++++++++++++++++++-- include/linux/pgtable.h | 11 ------ mm/filemap.c | 59 ++++++++++++++++++++++++++++---- mm/huge_memory.c | 14 ++++++++ 5 files changed, 102 insertions(+), 28 deletions(-) -- 2.52.0