linux-kernel - Re: [PATCHv3 1/1] block: introduce content activity based ioprio

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Date: Thu, 25 Jan 2024 15:52:16 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jens Axboe <axboe@...nel.dk>, Yu Zhao <yuzhao@...gle.com>, 
	Niklas Cassel <niklas.cassel@....com>, "Martin K . Petersen" <martin.petersen@...cle.com>, 
	Hannes Reinecke <hare@...e.de>, Linus Walleij <linus.walleij@...aro.org>, linux-mm@...ck.org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	steve.kang@...soc.com
Subject: Re: [PATCHv3 1/1] block: introduce content activity based ioprio

On Thu, Jan 25, 2024 at 3:40 PM Damien Le Moal <dlemoal@...nel.org> wrote:
>
> On 1/25/24 16:19, zhaoyang.huang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >
> > Currently, request's ioprio are set via task's schedule priority(when no
> > blkcg configured), which has high priority tasks possess the privilege on
> > both of CPU and IO scheduling.
> > This commit works as a hint of original policy by promoting the request ioprio
> > based on the page/folio's activity. The original idea comes from LRU_GEN
> > which provides more precised folio activity than before. This commit try
> > to adjust the request's ioprio when certain part of its folios are hot,
> > which indicate that this request carry important contents and need be
> > scheduled ealier.
> >
> > This commit is verified on a v6.6 6GB RAM android14 system via 4 test cases
> > by changing the bio_add_page/folio API in ext4 and f2fs.
>
> And as mentioned already by Chrisoph and Jens, why don't you just simply set
> bio->bi_ioprio to the value you want before calling submit_bio() in these file
> systems ? Why all the hacking of the priority code for that ? That is not
> justified at all.
>
> Furthermore, the activity things reduces the ioprio hint bits to the bare
> minimum 3 bits necessary for command duration limits. Not great. But if you
> simply set the prio class based on your activity algorithm, you do not need to
> change all that.
That is because bio->io_prio changes during bio grows with adding
different activity pages in. I have to wrap these into an API which
has both of fs and block be transparent to the process.
>
> Note: Your patch is full of whitespace changes.
Sorry, I double checked the source code and the patch with
checkpatch.pl again, no whitespace found, don't know why
>
> --
> Damien Le Moal
> Western Digital Research
>