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From:   Yang Shi <shy828301@gmail.com>
Date:   Fri, 6 Aug 2021 13:37:19 -0700
Message-ID: <CAHbLzkrqY=L2bEeEfAkApkoz=sRUk-Nk_KBDWGAbsqapY+xG1Q@mail.gmail.com>
Subject: Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()
To:     Hugh Dickins <hughd@google.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        "Huang, Ying" <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Minchan Kim <minchan@kernel.org>
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On Thu, Aug 5, 2021 at 11:01 PM Hugh Dickins <hughd@google.com> wrote:
>
> On Thu, 5 Aug 2021, Yang Shi wrote:
> > On Tue, Aug 3, 2021 at 10:34 PM Hugh Dickins <hughd@google.com> wrote:
> > >
> > > I've never seen the swapoff race claimed by Miaohe, and don't expect to;
> > > but he's probably right, given the current code.  I just dislike adding
> > > unnecessary complexity, and siting it in the wrong place (mm/shmem.c).
> > >
> > > Yang, is it possible that 5.1 commit 8fd2e0b505d1 ("mm: swap: check if
> > > swap backing device is congested or not") was actually developed and
> > > measured on 4.1 or earlier, which still had blk_set_queue_congested()?
> >
> > I forgot the exact version, but definitely not 4.1 or earlier. Maybe
> > 4.19 or earlier. I'm not familiar with how block layer detect
> > congestion, if the logic was changed, hence the optimization doesn't
> > stand anymore nowadays, I'm totally fine to remove it.
>
> You drove me back to look more closely.  blk_set_queue_congested()
> vanished from include/linux/blkdev.h in 4.2, but blk_set_congested()
> appeared then in block/blk-core.c to replace it.  blk_set_congested()
> vanished (along with all references to "congested" in blk-core.c) in
> 5.0, then your commit (most probably tested on 4.19) went into 5.1 -
> just after it had become redundant!
>
> Thanks, yes, let's revert that and Miaohe's and Huang's, later on.

It should be easier to revert Huang Ying's , then Miaohe's, then mine.

>
> Hugh