From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9C44736CDE3 for ; Thu, 9 Jul 2026 20:42:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783629733; cv=none; b=dk2xvV6+puHy0buKxeR+dbv5dlGlexkq/AUT7CO1lyvazMxwDWtTUO1lHqB4WHtqKfxItJop4/eoNa/KCP6aEwrgkVT0Vwaf6Uy5WQDqr4fR8lJhFZUY44tL+DBTufEZ9OXEBUbXplreT0+Wr8Z+RI2/V1UN/lvmWC1GNth9XYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783629733; c=relaxed/simple; bh=9Dasmo/bxQwXQ0OG2RX+p1IUv2pXpHnf7Orvv9NucxI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iVSEBo9JYrUHfc9RKejrYXWdmzEQmhDxDO6hhfAAzH2i/hhoDB7/ramfF6DRMD2ZSqCZ01wL0xwucf+BZN/fyiAhWuPiNfT48j77BZUcOkBt0QUv22giXEBiDHeoDxsQUvLFP4Zt2XTR+mKdsMPNAnXvB+/HhfswW/O7BVAJSd8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q0kaGcRC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Q0kaGcRC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9C6B1F000E9; Thu, 9 Jul 2026 20:42:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783629732; bh=eTaYGVr58Q84AkC+6dR6pRWmXzMoGmXAfHwB6T7z4YY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Q0kaGcRCjiqw2ou9rucxm9EOKU24drX4BWO0TDHjpAYNUO6uaB0L/E7HZw+/uzmn3 Po3F0xL3fw7Awa0DKL4IgX06GH399MjNm9n3zAQyLeEpE1i8kFSnEiUD3lpEnsAAxX NxHCrnJdDRkbxpZvmJTKTtwwJMsYdcYHrES8agVlS81g076Gl01R5Rtmzz+Oj5tiwe JzULGIwLoA9qLSNrYNfAgg8KNUZ+vI2KMGP53CSt53ZmaABc4Ho06wAd8MhQSRi/9i 7xoHZvqYZvb1//LN5KM5KKljl0V/0JyIQnoa4OA+IGylQiDqy0pA/qTbWfisrxE97c fQS42DwQLmY0A== Message-ID: Date: Thu, 9 Jul 2026 22:42:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] mm: compaction: support non-movable compaction for pageblock requests Content-Language: en-US To: Johannes Weiner Cc: Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260626182215.1107966-1-hannes@cmpxchg.org> <20260626182215.1107966-3-hannes@cmpxchg.org> <61bc1ad0-f9e3-405a-ae32-b89bcdd2e1d1@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/9/26 19:39, Johannes Weiner wrote: > On Thu, Jul 02, 2026 at 11:28:47AM +0200, Vlastimil Babka (SUSE) wrote: >> On 7/1/26 23:11, Johannes Weiner wrote: >> > On Wed, Jul 01, 2026 at 08:14:05PM +0200, Vlastimil Babka (SUSE) wrote: >> >> >> >> > This made the migratetype filtering about preventing block >> >> > pollution. The patch quotes reduced extfrag numbers. >> >> > >> >> > So now we have a block pollution guard that we apply only if... the >> >> > scanner is latency sensitive? :) Is this actually desired behavior? >> >> >> >> Yeah indeed I was wondering in this direction. >> >> >> >> > Another way of looking at it would be this: >> >> > >> >> > /* >> >> > * Allocation fallbacks can spread migratable pages >> >> > * into non-movable blocks. >> >> >> >> But also vice versa, non-movable pages into movable blocks? (without >> >> defrag_mode?). >> > >> > Uhm but those aren't compactable anymore then, right? >> >> Yeah. >> >> > There is a flipside, but it isn't quite symmetrical. Movable requests >> > are allowed to look for movables in unmovable blocks once they become >> > sync (high-effort, low-result). Non-movable requests are finally >> > allowed to empty movable blocks once they become sync; they *start* >> > with the high-effort, low-result mode to avoid block contamination but >> > are allowed to escalate when that doesn't produce results. >> >> Hm, true! >> >> I was also thinking, if defrag mode doesn't allow that escalation ever >> (IIRC?), should it be reflected here as well even with sync compaction? > > Ok I made a clarification regarding defrag_mode in the other comment. > > How about this? Looks good. > diff --git a/mm/compaction.c b/mm/compaction.c > index 7df3a85d43af..a12a49eefe85 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1399,13 +1399,24 @@ static bool suitable_migration_source(struct compact_control *cc, > if (is_migrate_cma(block_mt) && !(cc->alloc_flags & ALLOC_CMA)) > return false; > > + /* > + * Per default, scans are restricted to blocks compatible with > + * the request, to prevent cross-contamination. Once > + * compaction priority escalates to synchronous scans, though, > + * scan all blocks to try to make forward progress. For > + * movable request, this likely helps little: there shouldn't > + * be many migratable pages inside non-movable blocks besides > + * allocator fallbacks. For non-movable requests, this helps a > + * lot, as they can finally scan movable blocks. > + */ > if (cc->mode != MIGRATE_ASYNC) > return true; > > /* > * Prevent small unmovable/reclaimable requests from polluting > - * movable blocks through fallbacks. Whole-block production is > - * exempt as the allocator claims and converts these. > + * movable blocks through fallbacks. Whole-block production > + * (directly requested, or defrag_mode) is exempt as the > + * allocator claims and converts these. > */ > if (cc->migratetype == MIGRATE_MOVABLE || cc->order >= pageblock_order) > return is_migrate_movable(block_mt);