linux-kernel - Re: [PATCH RFC] mm: count zeromap read and set for swapout and swapin

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Message-ID: <CAKEwX=P2EKkbAgoUJ_RTRwv0DS18HfnEG2gRFmCYyb2R+LsrvA@mail.gmail.com>
Date: Mon, 28 Oct 2024 09:33:11 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Johannes Weiner <hannes@...xchg.org>, David Hildenbrand <david@...hat.com>, Hugh Dickins <hughd@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Andi Kleen <ak@...ux.intel.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Chris Li <chrisl@...nel.org>, "Huang, Ying" <ying.huang@...el.com>, 
	Kairui Song <kasong@...cent.com>, Ryan Roberts <ryan.roberts@....com>, joshua.hahnjy@...il.com
Subject: Re: [PATCH RFC] mm: count zeromap read and set for swapout and swapin

On Mon, Oct 28, 2024 at 5:23 AM Usama Arif <usamaarif642@...il.com> wrote:
>
> I wonder if instead of having counters, it might be better to keep track
> of the number of zeropages currently stored in zeromap, similar to how
> zswap_same_filled_pages did it. It will be more complicated then this
> patch, but would give more insight of the current state of the system.
>
> Joshua (in CC) was going to have a look at that.

I don't think one can substitute for the other.

The "current zeromapped page" counter gives you a breakdown of where
memory resides, whereas the in/out counters explain past performance
based on events that have happened. That's why you have zswap,
zswapped, zswpout, zswpin.