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From:   Chris Li <chrisl@kernel.org>
Date:   Sun, 19 Nov 2023 21:31:30 -0800
Message-ID: <CAF8kJuPs=O7dKQYWAyM5N1UPyCkEmaCb9REHmNvAi7o4tPbMDg@mail.gmail.com>
Subject: Re: [PATCH] mm:zswap: fix zswap entry reclamation failure in two scenarios
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     Yosry Ahmed <yosryahmed@google.com>,
        Zhongkun He <hezhongkun.hzk@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Nhat Pham <nphamcs@gmail.com>,
        Seth Jennings <sjenning@redhat.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Vitaly Wool <vitaly.wool@konsulko.com>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sun, Nov 19, 2023 at 7:20=E2=80=AFPM Huang, Ying <ying.huang@intel.com> =
wrote:
>
> Chris Li <chriscli@google.com> writes:
>
> > On Thu, Nov 16, 2023 at 12:19=E2=80=AFPM Yosry Ahmed <yosryahmed@google=
.com> wrote:
> > That will cancel the batching effect on the swap slot free, making the
> > common case for  swapping  faults take longer to complete, righ?
> > If I recall correctly, the uncharge is the expensive part of the swap
> > slot free operation.
> > I just want to figure out what we are trading off against. This is not
> > one side wins all situations.
>
> Per my understanding, we don't batch memcg uncharging in
> swap_entry_free() now.  Although it's possible and may improve
> performance.

swap_entry_free() does not do batching, it is at the caller level.

I just checked. The batching is done in free_swap_slot() is still
using swap slot cache and batching.
It uses swapcache_free_entries() to batch free the swap_slots. That is
where the uncharge happens per my understanding.

Chris