linux-kernel - Re: [PATCH] mm/zswap: Replace kmap_atomic() with kmap_local

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Message-ID: <CAF8kJuPNYpHy=5fTzH5b0RoDHfCQKLkJM_APtnUQ-bs=Y60mmg@mail.gmail.com>
Date:   Tue, 28 Nov 2023 12:43:26 -0800
From:   Chris Li <chrisl@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
        Nhat Pham <nphamcs@...il.com>
Subject: Re: [PATCH] mm/zswap: Replace kmap_atomic() with kmap_local_page()

Hi Matthew,

On Tue, Nov 28, 2023 at 6:09 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > >From the performance perspective, kmap_local_page() does less so it
> > has some performance gain. I am trying to think would it have another
> > unwanted side effect of enabling interrupt and page fault while zswap
> > decompressing a page.
> > The decompression should not generate page fault. The interrupt
> > enabling might introduce extra latency, but most of the page fault was
> > having interrupt enabled anyway. The time spent in decompression is
> > relatively small compared to the whole duration of the page fault. So
> > the interrupt enabling during those short windows should be fine.
> > "Should" is the famous last word.
>
> Interrupts are enabled with kmap_atomic() too.  The difference is
> whether we can be preempted by a higher-priority process.
>
You are right, thanks for the clarification.

Hi Fabio,

Acked-by: Chris Li <chrisl@...nel.org> (Google)

Chris