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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3DCFECD6E4A for ; Fri, 29 May 2026 12:36:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 62B316B0088; Fri, 29 May 2026 08:36:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5DC676B0092; Fri, 29 May 2026 08:36:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4F20B6B0095; Fri, 29 May 2026 08:36:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 44D7E6B0088 for ; Fri, 29 May 2026 08:36:29 -0400 (EDT) Received: from smtpin05.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id E2C5A1C0024 for ; Fri, 29 May 2026 12:36:28 +0000 (UTC) X-FDA: 84820405656.05.DD6D65F Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) by imf15.hostedemail.com (Postfix) with ESMTP id 8554EA000E for ; Fri, 29 May 2026 12:36:25 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=jjsu6Mlv; spf=pass (imf15.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780058187; h=from:from:sender: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:dkim-signature; bh=9lVmfgexspnKoW/3agaiDvDisr/iv75bUoYrdSLOXwE=; b=Ewz7SRv8WvhG9EgRMffveT9qZHASeyOlc0UCGPtqGhv81TT7k7r8T2R5JoNcGxkRglt8cH BSDhNLkCf8mjApDQeDWEVCB0khWfOe6f5zx9tCo5eMZLgyW5znJzo0sMwMoxljzTN03btT 3DMPyHhkfkwYUJvCURMr9be6NdFI1QU= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=jjsu6Mlv; spf=pass (imf15.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1780058187; a=rsa-sha256; cv=none; b=5TV1GPQROcX4xo048E54vm4OShSOIMalMgvKYc2ZaU4JWJKM0zOyJZ+w/kA/uCVAOgi3pj UILnQ1+gvYJke9A/CUQYNKbgDMXYAYwoWvTcStxkKgDi5FefzbuOvESV/6LDmQtfRBhsxJ 9i6+7fPc8KZN17lnoRH/mSvdybZjYeg= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780058181; 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=9lVmfgexspnKoW/3agaiDvDisr/iv75bUoYrdSLOXwE=; b=jjsu6MlvrjBVw8EHwN0hZmMlYdVyXnIGj7OspJTJ4D6N+7yBnvman4zcAHpc1Ij97Gm08b r/smJSHm1710yMUCteZUE0tkdOltvNb2M1Yl3SZ4d9zzKBzaKOzUGwE6mp49+rBFiVdWRH JYU2SGHM12nodC78Fy/TqrlxlFyboI8= Date: Fri, 29 May 2026 13:36:10 +0100 MIME-Version: 1.0 Subject: Re: [PATCH v6 2/2] mm: use mapping_max_folio_order() for force_thp_readahead order To: Andrew Morton , david@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org Cc: 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 , ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com References: <20260528165635.2068012-1-usama.arif@linux.dev> <20260528165635.2068012-3-usama.arif@linux.dev> 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: <20260528165635.2068012-3-usama.arif@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: uajust1hk36d89e4pbe744i58mo3iube X-Rspamd-Queue-Id: 8554EA000E X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1780058185-427254 X-HE-Meta: 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 /3++jHOh 9E5/JwcQ9kHqJ0isLWGDi/fmoTHuWILLy03nnWHFdqc0fsnoCime5GKBUfNtMcPbx434UpIVEmkYW4f6b3Fa9MjPt+/2DkTy0vQhuFBbNwdegqrodjQQLtNiNWJOM3kCqcxEWG4SflEMRWfJfRPeR/cF7PQy8AnC4XOC2BvWsXBdOvN1l8WiFXC3roVh08BoaEO/6YoVyGL9pM/ZpB7QcBrYu5n71dzBLLHdreAeINo5S7DE5wqOiT0aHSySPNyTqaKHXcaxRmYFAAFXKmZj4NeQsSIrF2AT/jttZZgVg/vUIa00CJVkox/Pg6aPaUa5II2T8crAq9lPwGzLMAdnHPF/Lqg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 28/05/2026 17:55, Usama Arif wrote: > The force_thp_readahead path in do_sync_mmap_readahead() is gated on > HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER and always requests > HPAGE_PMD_ORDER / HPAGE_PMD_NR. On configurations where HPAGE_PMD_ORDER > exceeds MAX_PAGECACHE_ORDER, notably arm64 with a 64K base page size, > VM_HUGEPAGE mappings cannot use this path and fall back to the non-forced > mmap readahead path even when the mapping supports useful large folios. > > Keep the existing PMD-sized behavior when HPAGE_PMD_ORDER fits in the > page cache. When it does not, enable forced readahead for mappings that > support large folios and request an order capped by both > mapping_max_folio_order(mapping) and 2MB. > > 2MB is chosen as the cap because it matches the PMD size on x86_64 > and on arm64 with 4K or 16K base pages, so the size/memory-pressure > tradeoff for folios of that size is already well understood. On arm64 > with a 64K base page size, 2MB is also the contiguous-PTE (contpte) > block size, so the resulting folios coalesce into a single TLB entry > and reduce TLB pressure on the readahead path. > > The final allocation order may still be clamped by page_cache_ra_order() > to the mapping and request geometry, but this gives VM_HUGEPAGE mappings > on such configurations a large-folio readahead request instead of > dropping back to base-page readahead. > > Signed-off-by: Usama Arif > --- > mm/filemap.c | 27 +++++++++++++++++++-------- > 1 file changed, 19 insertions(+), 8 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index a16b33e0fc71..bfb891d9da1f 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3312,14 +3312,23 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > struct file *fpin = NULL; > vm_flags_t vm_flags = vmf->vma->vm_flags; > bool force_thp_readahead = false; > + unsigned int thp_order = 0; > unsigned short mmap_miss; > > ractl._max_index = vmf->vma->vm_pgoff + vma_pages(vmf->vma) - 1; > > /* Use the readahead code, even if readahead is disabled */ > - if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && > - (vm_flags & VM_HUGEPAGE) && HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER) > - force_thp_readahead = true; > + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && (vm_flags & VM_HUGEPAGE)) { > + if (HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER) { > + force_thp_readahead = true; > + thp_order = HPAGE_PMD_ORDER; > + } else if (mapping_large_folio_support(mapping)) { > + force_thp_readahead = true; > + thp_order = min_t(unsigned int, > + mapping_max_folio_order(mapping), > + get_order(SZ_2M)); > + } > + } > I think might be good to include the below comment to explain the decision being made here: >From 6673c04a434df01d449c1bdb9ac8de74e19d6b7e Mon Sep 17 00:00:00 2001 From: Usama Arif Date: Fri, 29 May 2026 05:31:05 -0700 Subject: [PATCH] [fixlet] mm/filemap: add comment explaining design decision Signed-off-by: Usama Arif --- mm/filemap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index bfb891d9da1f..0a3facf452b3 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3319,6 +3319,14 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) /* Use the readahead code, even if readahead is disabled */ if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && (vm_flags & VM_HUGEPAGE)) { + /* + * Preserve PMD-sized readahead where it already fits in + * the page cache. Otherwise cap the new fallback path at + * 2MB: this is the common PMD-sized hugepage size, and it + * avoids memory pressure from very large forced readahead + * when mapping_max_folio_order() is high (for example, + * 128MB with 64K base pages on arm64). + */ if (HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER) { force_thp_readahead = true; thp_order = HPAGE_PMD_ORDER; -- 2.53.0-Meta