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

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Date:	Sat, 20 Dec 2014 11:25:57 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
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

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).

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.

Thanks.

> 
> Thanks.
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