linux-kernel - Re: [PATCH] zram: modernize writeback interface

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Message-ID: <iiav3vvvvu7lzcl3e2rzfh4kyz6kwymqurncjdsv62wvlge63k@ewgbdmzdnb2p>
Date: Wed, 26 Mar 2025 17:15:28 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Richard Chang <richardycc@...gle.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Minchan Kim <minchan@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Brian Geffon <bgeffon@...gle.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: modernize writeback interface

On (25/03/26 15:07), Richard Chang wrote:
> I am just counting how many pages we could writeback per syscall.
> In a worst case, page_index_range with several two-adjacent indices:
> Assume PAGE_SIZE is 4k and index range is around 10000,
> 
> page_index_range allows 272 pages per syscall:
> page_index_range=10000-10001 page_index_range=10003-10004...
> 
> List_range allows 678 pages per syscall:
> page_index_range=10000-10001,10003-10004...

Page index can be u32, much longer than 10000.  With really high
indices you'd probably waste more space on "N-N+1" alone than on
page_index=N.  I'd say index-range should be used when there is
a range to begin with.

[..]
> Another alternative thought, how about page_index supporting both
> single instance and ranges?
> The key is shorter and the parser is relatively simpler.
> Eg: page_index=500 page_index=10000-10001

I probably can look into it.