From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (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 B5BA635893 for ; Tue, 8 Sep 2026 04:01:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788840120; cv=none; b=f399yEFl3xLuknriHVvslAgRzfYeD77okwuZjthwXxE5VWmEvqvA+UODBmFKvJbV7dLIF1E95YtA1csKW2OszOKoPE1HClqDY4RetowT10VK1622Mv8APK4fUcvQh6NVty1jfHxgQ5GDfb9U+sAGdXErq7j2UsGt7dPwDeNitOg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788840120; c=relaxed/simple; bh=z5wLPDOqzDA0g4Zat4E1HFBuShjpvgZMQEsG4gIDtG4=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=thubWF0RgGwSTDV+vEHSKtgSjBNyAJ5qvS8YGSZWaeoAj7Y+ekhRlj/YVLifU5zKOfIP24WTn18RvGjvxwbGXOjRL+f3rnbhyiM66U4Q94ZxGe9sZxKACnIoYFPDJQn3kHIKfmgdhGfhI+YH1FNOqbJZBuq/FLiDOUF8X1g4KeU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=M9oOdwWt; arc=none smtp.client-ip=115.124.30.110 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="M9oOdwWt" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1788840108; h=Message-ID:Date:MIME-Version:Subject:From:To:Content-Type; bh=Najs9RGCkB+xTfIo5Ipvni0lhIFU34DcqdN/H9GY20E=; b=M9oOdwWtCAnh0m0XULvaX+L3CM8yp1ebQIvTYvIIvHvPYbgSUhg0uLLXDSrpvOG8ogRYFsjXF9HNlaW376vnR537N2xlD3qwizEeVZHpW07TX9MHgsQpuR5JVucd5XDNJMVgOzVyq1Ik/FbiLZ4lqDCW/ddVwOl8ICtM9MYo2CQ= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam011083073210;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=17;SR=0;TI=SMTPD_---0XAaJnml_1788840106; Received: from 30.74.144.127(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XAaJnml_1788840106 cluster:ay36) by smtp.aliyun-inc.com; Tue, 08 Sep 2026 12:01:47 +0800 Message-ID: <31494361-406e-4874-8a2c-2c6f5cee5321@linux.alibaba.com> Date: Tue, 8 Sep 2026 12:01:46 +0800 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] mm: mglru: clear the reference counter for rejected folios From: Baolin Wang To: Barry Song , Baoquan He Cc: akpm@linux-foundation.org, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, ljs@kernel.org, ridong.chen@linux.dev, hebaoquan@kylinos.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8e4db9a298c5ea6ccb192e274caed5b96f0cf022.1788751143.git.baolin.wang@linux.alibaba.com> <67d9bbcf-2991-4867-8afb-14bad1cebf8d@linux.alibaba.com> In-Reply-To: <67d9bbcf-2991-4867-8afb-14bad1cebf8d@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/8/26 11:03 AM, Baolin Wang wrote: > > > On 9/8/26 10:34 AM, Barry Song wrote: >> On Tue, Sep 8, 2026 at 10:30 AM Baoquan He wrote: >>> >>> Hi Baolin, >>> >>> On 09/07/26 at 11:25am, Baolin Wang wrote: >>> ......snip... >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 40d3f1b48a74..42c0a09938ab 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>> >>> Well, this seems to be based on Andrew's mm-new branch. I usually track >>> mm-unstable branch. Maybe the subject should be marked as below? >>> [PATCH mm-new] mm: mglru: clear the reference counter for rejected > > ACK. > >>> >>>> @@ -5021,10 +5021,11 @@ static int evict_folios(unsigned long >>>> nr_to_scan, struct lruvec *lruvec, >>>>                } >>>> >>>>                /* don't add rejected folios to the oldest generation */ >>>> -             if (lru_gen_folio_seq(lruvec, folio, false) == >>>> min_seq[type]) { >>>> -                     folio_set_lru_refs(folio, 0); >>>> +             if (lru_gen_folio_seq(lruvec, folio, false) == >>>> min_seq[type]) >>>>                        folio_set_active(folio); >>>> -             } >>>> + >>>> +             /* See the comments on LRU_REFS_FLAGS */ >>>> +             folio_set_lru_refs(folio, 0); >>> >>> This looks like a great catch, while the code change could bring issue. >>> >>> Because move_folios_to_lru() relies on folios' flags to decide their new >>> generation. You just cleared it before move_folios_to_lru(). This is no >>> problem for rejected folios that are determined to be put into the >>> oldest generation. But for those rejected folios that are determined to >>> be promoted, this could be wrong. E.g currently gen window is 4, and a >>> folio is referenced, lru_gen_folio_seq() decides its new gen as 1, which >>> is the 2nd oldest generation. While folio_set_lru_refs(folio, 0) clear >>> referenced bit, this causes it being put into the oldest generation in >>> move_folios_to_lru(), this is not expected. > > Yes. As I discussed with Barry earlier, lru_gen_folio_seq() also needs > to be reconsidered regarding whether it should rely on PG_referenced [1]. > > For commit 6cbdd9726fb5, we didn't discuss the impact on rejected folios > either. Before commit 6cbdd9726fb5, if rejected folios did not have > PG_active set by shrink_folio_list(), evict_folios() would set PG_active > on these rejected folios. > > [1] https://lore.kernel.org/linux-mm/20260901220430.79810-1- > baohua@kernel.org/ > >> The original code looks quite weird. It even prioritizes folios >> that won't be promoted by `PG_active`. Do we need to change all >> the cases just to call `PG_active`? > > Yes. Regarding this concern, I plan to change back to the original > behavior: > >     /* See the comments on LRU_REFS_FLAGS */ >     folio_set_lru_refs(folio, 0); > >     /* don't add rejected folios to the oldest generation */ >     if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]) >         folio_set_active(folio); > > What do you think? Just FYI, after above changes, the performance improvement on zram is no longer obvious either. I think this also answers Kairui's earlier question about why I saw a performance improvement (which seems related to commit 6cbdd9726fb5). Also, there is no obvious performance regression either. zram swap: w/o patch w/ patch sys time: 1666.5s 1628.5s