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 DF489572693; Wed, 9 Sep 2026 15:04:31 +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=1788966273; cv=none; b=My+MFDU1ANv0urvdMfPO49SzaV1XfURSEAszeBD5t3agcwvSUZ+8kuNlM8cfVzSCVRkTAQwNLfrTxE/xC9rBYPyh1Wv3SowzKMW1Nngi3DajXaJU1QeM7lPB1YFaFO0CsCIyKF8ApdXnUAdpyd9kGvWQe2xjjsd6xHVcBUnBZI0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788966273; c=relaxed/simple; bh=eyqrTym7YH33qhz2IUTjQgGLMwSrBBrEuGTGcohxOs8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GxOi9XiRn3fy9pU5xGP2Ak2+0yU/d7KoMvnLSgEXA8ob4+aZCB7XVoUhr73rmxG4KjtAmarBEO7WHHVYxoHbf9TtAQucT/D6apcun0InjsDqKunxrVu3kQuD8wEq0eWyrCI8mcaoUtWh8C0WMJE/KijrOkJlOoH2beF2IpdzmHw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SAcK3OrW; 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="SAcK3OrW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 82BC11F00A3D; Wed, 9 Sep 2026 15:04:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788966271; bh=aeXzLXfVC8e+tzbtM1PdBxXt6XZbDS/FpvLHCNUlfWg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SAcK3OrWdGIvBXHFshnW4N1kmYi8uwxh70A6GyDCuxzs3FrmYJeKrYDCHVjEu2pmw UIZKF5N1faibN8kfZYJSfF5CU0Dibdmu/VfarSip3jGeg3La2SN17ZRb6kR4YVvsot nQBn/sJrXnnzCKvNgRfFOdliI3BHkx1Ijv5u+yF5K2mxhLL29fk6n2Ubh6H215S+2u ztCV5CLMnDkfxc7sSS0yPfugcoX62t41N/Mi36hA5mdjlUYs/CSFuPjQV3hsoJOekf blBoiFCh2VK5IXhrzqYxtDOLjqBw5HErG+DVT55hQ7Yik6LSawqEn0JIz4cOub2UYd c+QYLaq1P1OqQ== Message-ID: Date: Wed, 9 Sep 2026 17:04:21 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 05/26] mm/fbatch: lru_add_del_folio()+folio_add_lru() after clear_lru() Content-Language: en-US To: Hugh Dickins , Andrew Morton Cc: Ackerley Tng , Alexander Viro , Alexandre Ghiti , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , Claudio Imbrenda , David Hildenbrand , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: 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 9/9/26 11:51, Hugh Dickins wrote: > Most callers of folio_test_clear_lru() then proceed to remove the folio > from its lru, and add it back at the end when they're done (if still in > use). But isolate_migratepages_block() and check_move_unevictable_pages() > sometimes decide against, and release immediately with a folio_set_lru(). > > Which usually works fine: but there's now a small chance that while they > held the folio with lru bit cleared, an lru_add fbatch drain came along, > and had to skip that folio because its lru bit was transiently cleared > (previously, the lru_add fbatch drain relied on finding lru bit never yet > set). This risks leaving that folio off lru, unreclaimable until freed. So this makes the previous patch a somewhat bisection hazard? I guess it's acceptable given it's not fatal. > Fix such cases by trying lru_add_del_folio() (which only takes action and > returns true if the folio was on an lru_add fbatch), then folio_add_lru() Oh ok, that's one detail I didn't realize on the previous patch, and explains the name of the function. But it's still IMHO confusing. > if it succeeded: invalidating the old fbatch slot, appending in a new one. > > Signed-off-by: Hugh Dickins In general, LGTM. Reviewed-by: Vlastimil Babka (SUSE) Nit below: > --- > mm/compaction.c | 13 +++++++++++-- > mm/vmscan.c | 16 +++++++++------- > 2 files changed, 20 insertions(+), 9 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index a049415512c6..9e045a90ba21 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1204,7 +1204,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > !cc->alloc_contig)) { > low_pfn += folio_nr_pages(folio) - 1; > nr_scanned += folio_nr_pages(folio) - 1; > - folio_set_lru(folio); > + if (lru_add_del_folio(folio)) { > + lruvec_unlock_irqrestore(locked, flags); > + folio_add_lru(folio); > + locked = NULL; > + } else { > + folio_set_lru(folio); > + } > goto isolate_fail_put; > } > } > @@ -1293,7 +1299,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > if (locked) > lruvec_unlock_irqrestore(locked, flags); > if (folio) { > - folio_set_lru(folio); > + if (lru_add_del_folio(folio)) > + folio_add_lru(folio); > + else > + folio_set_lru(folio); > folio_put(folio); > } > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f11491ee9ed5..4e8d5cc34f07 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -8093,17 +8093,19 @@ void check_move_unevictable_folios(struct folio_batch *fbatch) > folio_clear_unevictable(folio); > lruvec_add_folio(lruvec, folio); > pgrescued += nr_pages; > + } else if (lru_add_del_folio(folio)) { > + lruvec_unlock_irq(lruvec); > + folio_add_lru(folio); > + lruvec = NULL; > } > - folio_set_lru(folio); > + if (lruvec) > + folio_set_lru(folio); > } > > - if (lruvec) { > - __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); > - __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); > + if (lruvec) > lruvec_unlock_irq(lruvec); > - } else if (pgscanned) { > - count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); > - } > + count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); > + count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); AFAIU this is done because we can no longer rule out that !lruvec means pgrescued is 0. But we can still distinguish the cheaper __count_vm_events vs count_vm_events? Probably all the same on x86, but I hear on arm64 this_cpu* ops have a cost worth proposing rather elaborate schemes to deal with... > } > EXPORT_SYMBOL_GPL(check_move_unevictable_folios); >