linux-kernel - Re: [PATCH 3/5] mm/zswap: refactor out __zswap

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Date: Mon, 18 Dec 2023 01:38:04 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Nhat Pham <nphamcs@...il.com>, 
	Chris Li <chriscli@...gle.com>, Johannes Weiner <hannes@...xchg.org>, 
	Seth Jennings <sjenning@...hat.com>, Dan Streetman <ddstreet@...e.org>, 
	Vitaly Wool <vitaly.wool@...sulko.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/5] mm/zswap: refactor out __zswap_load()

On Mon, Dec 18, 2023 at 12:15 AM Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> On 2023/12/14 08:52, Yosry Ahmed wrote:
> > On Tue, Dec 12, 2023 at 8:18 PM Chengming Zhou
> > <zhouchengming@...edance.com> wrote:
> >>
> >> The zswap_load() and zswap_writeback_entry() have the same part that
> >> decompress the data from zswap_entry to page, so refactor out the
> >> common part as __zswap_load(entry, page).
> >>
> >> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> >> Reviewed-by: Nhat Pham <nphamcs@...il.com>
> >
> > On a second look, there a few nits here.
> >
> > First I think it makes more sense to move this refactoring ahead of
> > reusing destmem. Right now, we add the destmem reuse to zswap_load()
> > only, then we do the refactor and zswap_writeback_entry() gets it
> > automatically, so there is a slight change coming to
> > zswap_writeback_entry() hidden in the refactoring patch.
> >
> > Let's refactor out __zswap_load() first, then reuse destmem in it.
>
> I tried but found that putting the __zswap_load() first would introduce
> another failure case in zswap_writeback_entry(), since the temporary
> memory allocation may fail.
>
> So instead, I also move the dstmem reusing in zswap_writeback_entry() to
> the dstmem reusing patch. Then this patch becomes having only refactoring.

We could have still refactored __zswap_load() first by making it
return an int initially when split, then void later. Anyway, it's not
a big deal. The new series looks fine.