linux-kernel - Re: [PATCH v1 2/2] zram: remove init_lock in zram_make

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Date:	Thu, 29 Jan 2015 16:08:35 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request

On (01/29/15 15:35), Minchan Kim wrote:
>
> As you told, the data was not stable.
>
yes. fread test was always slower, and the rest was mostly slower.


> Anyway, when I read down_read implementation, it's one atomic instruction.
> Hmm, it seems te be better for srcu_read_lock which does more things.
>
srcu looks havier, agree.

> But I guessed most of overhead are from [de]compression, memcpy, clear_page
> That's why I guessed we don't have measurable difference from that.
> What's the data pattern if you use iozone?

by "data pattern" you mean usage scenario? well, I usually use zram for
`make -jX', where X=[4..N]. so N concurrent read-write ops scenario.

	-ss

> I guess it's really simple pattern compressor can do fast. I used /dev/sda
> for dd write so more realistic data. Anyway, if we has 10% regression even if
> the data is simple, I never want to merge it.
> I will test it carefully and if it turns out lots regression,
> surely, I will not go with this and send the original patch again.
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