From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6EE8CD5BB1 for ; Mon, 25 May 2026 15:02:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=AzwE9k9QJF7DUyRnk+qmGDQkXJ2+kA/q8Ntjxx3//vI=; b=2zDpvB6p+EOJ64rm4sUqgU+VKe yLlyYDB0ztlgOsvlxORerhFnSLQamXNzqBclEOXcb4aSBNCAco41L6kaC5WEe/mG8t22n4OTKLJ6D mOn7wEuaS3CIbPPKqT0UIC2xeuB5pGu2tDdZGrYkC/8nMSlJ6RSiTgCcYnr9tsuLRuWWl1B4IYOxW n7nUzEXKKdqtx4zzAqJKnDDa+u5/LF8XcesruGefxoyZbLTgpWchfJvnibB8ZX1lef3t/KJRtQmt8 JAcla639utZ+pvRciibmz6JgFQ2aIjWlLaeg+DgzSj815AkisYMBFSvGdsqRZuziVKd9DrGtig+hO yER3SuSQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wRWor-0000000HTdq-09dX; Mon, 25 May 2026 15:02:17 +0000 Received: from out-173.mta0.migadu.com ([91.218.175.173]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wRWon-0000000HTa7-44of for linux-arm-kernel@lists.infradead.org; Mon, 25 May 2026 15:02:15 +0000 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260525_080214_164795_4D0B4EAC X-CRM114-Status: GOOD ( 15.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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/