linux-kernel - Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks

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Date:   Sat, 30 Apr 2022 01:34:58 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     zhong jiang <zhongjiang-ali@...ux.alibaba.com>
Cc:     Stephen Rothwell <sfr@...hwell.id.au>,
        Linux-MM <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Barry Song <21cnbao@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Steven Barrett <steven@...uorix.net>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Daniel Byrne <djbyrne@....edu>,
        Donald Carr <d@...os-reins.com>,
        Holger Hoffstätte <holger@...lied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>,
        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks

On Fri, Apr 29, 2022 at 7:10 AM zhong jiang
<zhongjiang-ali@...ux.alibaba.com> wrote:
>
> On 2022/4/7 11:15 上午, Yu Zhao wrote:
...
> > +     while (!mm && mm_state->head != &mm_list->fifo) {
> > +             mm = list_entry(mm_state->head, struct mm_struct, lru_gen.list);
> > +
> > +             mm_state->head = mm_state->head->next;
> > +
> > +             /* full scan for those added after the last iteration */
> > +             if (!mm_state->tail || mm_state->tail == &mm->lru_gen.list) {
> > +                     mm_state->tail = mm_state->head;
> > +                     walk->full_scan = true;
> > +             }
> > +
>
> The full_scan seems to be alway true.   because mm_state->tail points to
> the first item in mm_list,  hence the walker's
>
> condition mm_state->tail == &mm->lru_gen.list alway equal.  Am I missing
> something?

mm_state->tail points to the first item *added after the last
iteration*. If no new items, mm_state->tail parks at mm_list->fifo.