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 <ed714a8c-4f36-0b86-0b36-c6708d6f26fb@linux.alibaba.com>
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From:   Yu Zhao <yuzhao@google.com>
Date:   Sat, 30 Apr 2022 01:34:58 -0700
Message-ID: <CAOUHufbPoxd=GrYR721dcrgf58UH1kqBp3X74Cw-OtdeTdiBWg@mail.gmail.com>
Subject: Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks
To:     zhong jiang <zhongjiang-ali@linux.alibaba.com>
Cc:     Stephen Rothwell <sfr@rothwell.id.au>,
        Linux-MM <linux-mm@kvack.org>, Andi Kleen <ak@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Aneesh Kumar <aneesh.kumar@linux.ibm.com>,
        Barry Song <21cnbao@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
        Jesse Barnes <jsbarnes@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Michael Larabel <Michael@michaellarabel.com>,
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        =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= <holger@applied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@yandex.ru>,
        Shuang Zhai <szhai2@cs.rochester.edu>,
        Sofia Trinh <sofia.trinh@edi.works>,
        Vaibhav Jain <vaibhav@linux.ibm.com>
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On Fri, Apr 29, 2022 at 7:10 AM zhong jiang
<zhongjiang-ali@linux.alibaba.com> wrote:
>
> On 2022/4/7 11:15 =E4=B8=8A=E5=8D=88, Yu Zhao wrote:
...
> > +     while (!mm && mm_state->head !=3D &mm_list->fifo) {
> > +             mm =3D list_entry(mm_state->head, struct mm_struct, lru_g=
en.list);
> > +
> > +             mm_state->head =3D mm_state->head->next;
> > +
> > +             /* full scan for those added after the last iteration */
> > +             if (!mm_state->tail || mm_state->tail =3D=3D &mm->lru_gen=
.list) {
> > +                     mm_state->tail =3D mm_state->head;
> > +                     walk->full_scan =3D 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 =3D=3D &mm->lru_gen.list alway equal.  Am I miss=
ing
> 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.