linux-kernel - Re: [RFC PATCHv5 0/6] zram: introduce writeback bio batching

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Message-ID: <upyms2wnksojg6ix7dha74bjm2gfhv6ieef65k3f2our4r6fp4@kjtpmu4mtbay>
Date: Fri, 21 Nov 2025 16:32:27 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yuwen Chen <ywen.chen@...mail.com>
Cc: senozhatsky@...omium.org, akpm@...ux-foundation.org, 
	bgeffon@...gle.com, licayy@...look.com, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, minchan@...nel.org, richardycc@...gle.com
Subject: Re: [RFC PATCHv5 0/6] zram: introduce writeback bio batching

On (25/11/21 15:14), Yuwen Chen wrote:
> On Fri, 21 Nov 2025 00:21:20 +0900, Sergey Senozhatsky wrote:
> > This is a different approach compared to [1].  Instead of
> > using blk plug API to batch writeback bios, we just keep
> > submitting them and track available of done/idle requests
> > (we still use a pool of requests, to put a constraint on
> > memory usage).  The intuition is that blk plug API is good
> > for sequential IO patterns, but zram writeback is more
> > likely to use random IO patterns.
> 
> > I only did minimal testing so far (in a VM).  More testing
> > (on real H/W) is needed, any help is highly appreciated.
> 
> I conducted a test on an NVMe host. When all requests were random,
> this fix was indeed a bit faster than the previous one.

Is "before" blk-plug based approach and "after" this new approach?

> before:
> real	0m0.261s
> user	0m0.000s
> sys	0m0.243s
> 
> real	0m0.260s
> user	0m0.000s
> sys	0m0.244s
> 
> real	0m0.259s
> user	0m0.000s
> sys	0m0.243s
> 
> after:
> real	0m0.322s
> user	0m0.000s
> sys	0m0.214s
> 
> real	0m0.326s
> user	0m0.000s
> sys	0m0.206s
> 
> real	0m0.325s
> user	0m0.000s
> sys	0m0.215s

Hmm that's less than was anticipated.