linux-kernel - Re: [PATCH v3 1/2] mm: store zero pages to be swapped out in a bitmap

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Message-ID: <Zmb6r6vrP2UTDQrK@casper.infradead.org>
Date: Mon, 10 Jun 2024 14:07:59 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Usama Arif <usamaarif642@...il.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, david@...hat.com,
	ying.huang@...el.com, hughd@...gle.com, yosryahmed@...gle.com,
	nphamcs@...il.com, chengming.zhou@...ux.dev, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v3 1/2] mm: store zero pages to be swapped out in a bitmap

On Mon, Jun 10, 2024 at 01:15:59PM +0100, Usama Arif wrote:
> +	if (is_folio_zero_filled(folio)) {
> +		swap_zeromap_folio_set(folio);
> +		folio_start_writeback(folio);
> +		folio_unlock(folio);
> +		folio_end_writeback(folio);

What's the point?  As far as I can see, the only thing this is going to
do is spend a lot of time messing with various counters only to end up
with incrementing NR_WRITTEN, which is wrong because you didn't actually
write it.