linux-kernel - Re: [PATCH v2] mm/zsmalloc: add statistics support

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Date:	Tue, 23 Dec 2014 10:26:12 +0800
From:	Ganesh Mahendran <opensource.ganesh@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>, Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/zsmalloc: add statistics support

Hello Minchan

2014-12-20 10:25 GMT+08:00 Minchan Kim <minchan@...nel.org>:
> Hey Ganesh,
>
> On Sat, Dec 20, 2014 at 09:43:34AM +0800, Ganesh Mahendran wrote:
>> 2014-12-20 8:23 GMT+08:00 Minchan Kim <minchan@...nel.org>:
>> > On Fri, Dec 19, 2014 at 04:17:56PM -0800, Andrew Morton wrote:
>> >> On Sat, 20 Dec 2014 09:10:43 +0900 Minchan Kim <minchan@...nel.org> wrote:
>> >>
>> >> > > It involves rehashing a lengthy argument with Greg.
>> >> >
>> >> > Okay. Then, Ganesh,
>> >> > please add warn message about duplicaed name possibility althoug
>> >> > it's unlikely as it is.
>> >>
>> >> Oh, getting EEXIST is easy with this patch.  Just create and destroy a
>> >> pool 2^32 times and the counter wraps ;) It's hardly a serious issue
>> >> for a debugging patch.
>> >
>> > I meant that I wanted to change from index to name passed from caller like this
>> >
>> > zram:
>> >         zs_create_pool(GFP_NOIO | __GFP_HIGHMEM, zram->disk->first_minor);
>> >
>> > So, duplication should be rare. :)
>>
>> We still can not know whether the name is duplicated if we do not
>> change the debugfs API.
>> The API does not return the errno to us.
>>
>> How about just zsmalloc decides the name of the pool-id, like pool-x.
>> When the pool-id reaches
>> 0xffff.ffff, we print warn message about duplicated name, and stop
>> creating the debugfs entry
>> for the user.
>
> The idea is from the developer point of view to implement thing easy
> but my point is we should take care of user(ie, admin) rather than
> developer(ie, we).

Yes. I got it.

>
> For user, /sys/kernel/debug/zsmalloc/zram0 would be more
> straightforward and even it doesn't need zram to export
> /sys/block/zram0/pool-id.

BTW, If we add a new argument in zs_create_pool(). It seems we also need to
add argument in zs_zpool_create(). So, zpool/zswap/zbud will be
modified to support
the new API.
Is that acceptable?

Thanks.

>
> Thanks.
>
>>
>> Thanks.
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