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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 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 92E21140011 X-Stat-Signature: x6zxk69bjkps7fj7crbujga61hc1x7aa X-Rspam-User: X-HE-Tag: 1788966272-24531 X-HE-Meta: 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 RVLHywlR Ji6vZpchgkUj0rQri9PYnlZQZKwUJVfX6anPgtqBAezg+e9LxcKMJDr5vRXEA/rgFqOWso+Q93FzbAA4wsh0N7M9DWNZBnV6+WHPwdcDN7jioSNRjHSnByfoxuixZ4ZmFDOha03LBDCdL11qFlC+rakWW8r/8lTZmongZY/vXd0LPT6ZAgHuVX/QwDjCjRTe4YeYtve/30DcYNXwq2l7vPaFGmnuOGwm30GsZkBYv5sRB29ikyH4QUqZX+L9aGlHs9YP/nf1IkcIjeoU0n137lyjSPsb10ymu/nKJXWnzOdDp6/BgLbDOcchdI9ut4L5roNDv4Roh74Vz/IVjwxg1qssY+ETo7LtNi+fggPsiDGq2W1iCC1nKIM0UVQahPJBOGuuKQrvvbPeP+Bjz/odq87oY8huYU0m+d01POAYAZ9UzhWk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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); >