linux-kernel - Re: [PATCH] zram: Add a huge

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Message-ID: <YjDMo35Q/cvPLkxu@casper.infradead.org>
Date:   Tue, 15 Mar 2022 17:28:03 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Brian Geffon <bgeffon@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-block@...r.kernel.org, linnux-mm@...ck.org
Subject: Re: [PATCH] zram: Add a huge_idle writeback mode

On Tue, Mar 15, 2022 at 10:22:21AM -0700, Brian Geffon wrote:
> Today it's only possible to write back as a page, idle, or huge.
> A user might want to writeback pages which are huge and idle first
> as these idle pages do not require decompression and make a good
> first pass for writeback.

We're moving towards having many different sizes of page in play,
not just PMD and PTE sizes.  Is this patch actually a good idea in
a case where we have, eg, a 32kB anonymous page on a system with 4kB
pages?  How should zram handle this case?  What's our cut-off for
declaring a page to be "huge"?