From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (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 34CCF2E424F for ; Mon, 25 May 2026 15:01:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779721308; cv=none; b=pSJWHzcOUzwT2noEqH/2Onqu3Cz24Sp8TolKKyYXy4if3k7h0VCz7FuBa6FJuuaN6WR+A8dntFvoxEScQK5ZTopYccS7rRrxTP+2eMfFUErKYdZkzTWHfEZR/NMCHBUr+bYOtwTIsNeNnZDFQczF0UgcEiqELgeMVwYBwaceUZo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779721308; c=relaxed/simple; bh=HFbkS0uEydiczYh7P5tXmXKuDdgk9/k4vID1HeaNMOs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=i1W1SvR2DRPlE2UHlvAp9PCsC4NoiREkswD+Ci+4x4uLGlSL8oSDfOzmLTXRLiZcFn7GC4IkFmLGwAp7s/rghhzGBvv59M4F70V1UFfB73Ufr4IFGwzYH7UtNhXVF3Rl4cBvlXfr20qJMn11rT6yDUg7x01558utdtG4Sc2HNWU= 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=fsSvL3R+; arc=none smtp.client-ip=91.218.175.172 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="fsSvL3R+" Message-ID: <8edc8cd0-f65c-4456-9b3f-362e744c9a96@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779721303; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AzwE9k9QJF7DUyRnk+qmGDQkXJ2+kA/q8Ntjxx3//vI=; b=fsSvL3R+HyOLiJBlzetIGjmPzu1GfueYA9lAtGy2Z8SL3+P0kPz1vyGsKd+ewF7+yPqqfC /iuy4xlG2sBfvGWm8UGvpe2AWMCyGuQUPrUGljCAmlQ3kSIJHpayjMw01YvtZ7vJP62/sE FqH9kKksxanHmBQ196JOJTJSIlyErtA= Date: Mon, 25 May 2026 16:01:19 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v5 0/2] mm: improve large folio readahead for exec memory To: Andrew Morton Cc: david@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org, r@hev.cc, jack@suse.cz, Andrew Donnellan , 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" , 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 , wilts.infradead.org@hp2.hsd1.ca.comcast.net, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com References: <20260522162422.3856502-1-usama.arif@linux.dev> <20260522122052.7b4ad7c482a0e4826296e392@linux-foundation.org> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Usama Arif In-Reply-To: <20260522122052.7b4ad7c482a0e4826296e392@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 22/05/2026 20:20, Andrew Morton wrote: > On Fri, 22 May 2026 09:23:46 -0700 Usama Arif wrote: > >> Two checks in do_sync_mmap_readahead() limit large-folio readahead: >> >> 1. The mmap_miss heuristic is meant to throttle wasteful speculative >> readahead. It is currently also applied to the VM_EXEC readahead >> path, which is targeted rather than speculative. Once mmap_miss exceeds >> MMAP_LOTSAMISS, exec readahead - including the large-folio >> order requested by exec_folio_order() - is disabled. On >> configurations where the mmap_miss decrement paths are not >> active (see patch 1) the counter only grows, so exec readahead >> is permanently disabled after the first 100 faults. >> >> 2. The force_thp_readahead path is gated only on >> HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER and always drives the >> readahead at HPAGE_PMD_ORDER. Configurations where >> HPAGE_PMD_ORDER exceeds MAX_PAGECACHE_ORDER never reach this >> path, even when the mapping itself supports usefully large >> folios well below the cap. >> >> Both issues are most visible on arm64 with a 64K base page size, >> where HPAGE_PMD_ORDER is 13 (512MB) -- above MAX_PAGECACHE_ORDER >> (11) -- and where fault_around_pages collapses to 1 disabling >> should_fault_around() (one of the two mmap_miss decrement sites). >> However the fixes are architecture-agnostic: patch 1 reflects the >> nature of VM_EXEC readahead regardless of base page size, and >> patch 2 generalises the gate so any mapping advertising a usefully >> large maximum folio order can benefit. >> >> 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 > > Well that's nice. > > AI review might have found a few things: > https://sashiko.dev/#/patchset/20260522162422.3856502-1-usama.arif@linux.dev > Thanks Andrew! So sashiko seems to have brought out some interesting problems, some of which are pre-existing. For example, the decrement sites for mmap_miss in do_async_mmap_readahead() and filemap_map_pages() dont skip for VM_SEQ_READ. I have sent this as an independent patch in [1]. I will send the next version of this series on top of [1] in a few days addressing the rest of the issues raised by sashiko. [1] https://lore.kernel.org/all/20260525145751.2671248-1-usama.arif@linux.dev/