Re: [PATCH v3 4/9] mm/swapcache: support to handle the value in swapcache

From: Joonsoo Kim <js1304@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@kernel.org>, Hugh Dickins <hughd@google.com>,
	Minchan Kim <minchan@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Mel Gorman <mgorman@techsingularity.net>,
	kernel-team@lge.com, Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v3 4/9] mm/swapcache: support to handle the value in swapcache
Date: Thu, 19 Mar 2020 15:01:03 +0900	[thread overview]
Message-ID: <CAAmzW4M2wqA4kJ7rzR7GsoS72krQRZx5i53jZh2uGikmVWLntQ@mail.gmail.com> (raw)
In-Reply-To: <20200318183318.GD154135@cmpxchg.org>

2020년 3월 19일 (목) 오전 3:33, Johannes Weiner <hannes@cmpxchg.org>님이 작성:
>
> On Tue, Mar 17, 2020 at 02:41:52PM +0900, js1304@gmail.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> > Swapcache doesn't handle the value since there is no case using the value.
> > In the following patch, workingset detection for anonymous page will be
> > implemented and it stores the value into the swapcache. So, we need to
> > handle it and this patch implement handling.
>
> "value" is too generic, it's not quite clear what this refers to
> here. "Exceptional entries" or "shadow entries" would be better.

Okay. Will change it.

> > @@ -155,24 +163,33 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
> >   * This must be called only on pages that have
> >   * been verified to be in the swap cache.
> >   */
> > -void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
> > +void __delete_from_swap_cache(struct page *page,
> > +                     swp_entry_t entry, void *shadow)
> >  {
> >       struct address_space *address_space = swap_address_space(entry);
> >       int i, nr = hpage_nr_pages(page);
> >       pgoff_t idx = swp_offset(entry);
> >       XA_STATE(xas, &address_space->i_pages, idx);
> >
> > +     /* Do not apply workingset detection for the hugh page */
> > +     if (nr > 1)
> > +             shadow = NULL;
>
> Hm, why is that? Should that be an XXX/TODO item? The comment should
> explain the reason, not necessarily what the code is doing.

It was my TODO. Now, I check the code and find that there is no blocker
for the huge page support. So, I will remove this code and enable the
workingset detection even for the huge page.

> Also, s/hugh/huge/

Okay.

> The rest of the patch looks straight-forward to me.

Thanks.