linux-kernel - Re: [PATCH] zram: set zram bio priority to REQ

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Date:   Tue, 18 Jul 2023 16:49:29 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Huanpeng Xin <xinhuanpeng9@...il.com>
Cc:     minchan@...nel.org, ngupta@...are.org, axboe@...nel.dk,
        senozhatsky@...omium.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, xinhuanpeng <xinhuanpeng@...omi.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] zram: set zram bio priority to REQ_PRIO.

Cc-ing Christoph

On (23/07/18 15:11), Huanpeng Xin wrote:
> 
> When the system memory pressure is high, set zram bio priority
> to REQ_PRIO can quickly swap zarm's memory to backing device,

read_from_bdev_async() does the opposite.

[..]
> @@ -616,7 +616,7 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
>  {
> +	bio = bio_alloc(zram->bdev, 1, parent ? parent->bi_opf : REQ_OP_READ | REQ_PRIO,
>  			GFP_NOIO);

[..]

> @@ -746,7 +746,7 @@ static ssize_t writeback_store(struct device *dev,
> ...
>  		bio_init(&bio, zram->bdev, &bio_vec, 1,
> -			 REQ_OP_WRITE | REQ_SYNC);
> +			 REQ_OP_WRITE | REQ_SYNC | REQ_PRIO);

In general, zram writeback is not for situations when the system
is critically low on memory; performance there is not that important,
so I'm not sure whether we want to boost requests' priorities.