From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 75DBC1391 for ; Sat, 20 Dec 2025 22:16:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766268963; cv=none; b=VBCcl9aSViv2XFvtaoQAux1yIHTok4vlNqJuR5nttNCxHVYRRgQFbplCXTatl3rum/dIjRgZQbr8W8wiif3rQt5Vi3Xv7qnSgrJvvNflZPC8MW5fh0ewOYRbelzpcdBrxMsF8Q+b19U1jzzqQpnn8AMfo5MH+KhaT08+wl8IiEw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766268963; c=relaxed/simple; bh=eDFY+632LEAOsKRJQQq/wHU8+MniI96pKzXiKyVhIkY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=VYB9Z/WiZAbKUoqyK1nzHucuzYwe14FIjiYwNJo3HfMbIU8VUXdVoeFXXGKuBOGOhGCThRapMxipna32aES14lHBu1s4T/N6YULawTTeTeIGwYnsxcckLDNgZK2UmXoYo0jm/6RafcpOQdPI89oUNSGGu4KkoxDJ3+wzChbkhLQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=tMGSOVJ7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="tMGSOVJ7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AEF2C4CEF5; Sat, 20 Dec 2025 22:16:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1766268962; bh=eDFY+632LEAOsKRJQQq/wHU8+MniI96pKzXiKyVhIkY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=tMGSOVJ7fM4y8KXLFuhaX2f5FOSPRx0b6ITrdy79OyMHzpfKgj80TDa1iNtP1h0hS Oi28VPjZ6bMikXlAoTV9sPDM/2ovWxHFfb3frc0jxT+ofRcfo6k73rd96Xc8vpJ7lk SqDcTC10OvCyvSESmjkP2gGuXSamET7nJnv+amSk= Date: Sat, 20 Dec 2025 14:16:01 -0800 From: Andrew Morton To: Vlastimil Babka Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , David Rientjes , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Joshua Hahn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm, page_alloc, thp: prevent reclaim for __GFP_THISNODE THP allocations Message-Id: <20251220141601.e6694f904167bf12fa319a89@linux-foundation.org> In-Reply-To: <20251219-costly-noretry-thisnode-fix-v1-1-e1085a4a0c34@suse.cz> References: <20251219-costly-noretry-thisnode-fix-v1-1-e1085a4a0c34@suse.cz> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 19 Dec 2025 17:31:57 +0100 Vlastimil Babka wrote: > Since commit cc638f329ef6 ("mm, thp: tweak reclaim/compaction effort of > local-only and all-node allocations"), THP page fault allocations have > settled on the following scheme (from the commit log): > > 1. local node only THP allocation with no reclaim, just compaction. > 2. for madvised VMA's or when synchronous compaction is enabled always - THP > allocation from any node with effort determined by global defrag setting > and VMA madvise > 3. fallback to base pages on any node > > Recent customer reports however revealed we have a gap in step 1 above. > What we have seen is excessive reclaim due to THP page faults on a NUMA > node that's close to its high watermark, while other nodes have plenty > of free memory. > > The problem with step 1 is that it promises no reclaim after the > compaction attempt, however reclaim is only avoided for certain > compaction outcomes (deferred, or skipped due to insufficient free base > pages), and not e.g. when compaction is actually performed but fails (we > did see compact_fail vmstat counter increasing). > > THP page faults can therefore exhibit a zone_reclaim_mode-like behavior, > which is not the intention. > > Thus add a check for __GFP_THISNODE that corresponds to this exact > situation and prevents continuing with reclaim/compaction once the > initial compaction attempt isn't successful in allocating the page. > > Note that commit cc638f329ef6 has not introduced this over-reclaim > possibility; it appears to exist in some form since commit 2f0799a0ffc0 > ("mm, thp: restore node-local hugepage allocations"). Followup commits > b39d0ee2632d ("mm, page_alloc: avoid expensive reclaim when compaction > may not succeed") and cc638f329ef6 have moved in the right direction, > but left the abovementioned gap. Cool. What are your thoughts on which kernel version(s) should receive this?