linux-kernel - Re: [PATCH 1/1] zram: better utilization of zram swap space

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Date:   Fri, 8 Dec 2017 15:11:25 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Gopi Sai Teja <gopi.st@...sung.com>, minchan@...nel.org,
        ngupta@...are.org, linux-kernel@...r.kernel.org,
        v.narang@...sung.com, pankaj.m@...sung.com, a.sahrawat@...sung.com,
        prakash.a@...sung.com, himanshu.sh@...sung.com
Subject: Re: [PATCH 1/1] zram: better utilization of zram swap space

On (12/07/17 17:45), Sergey Senozhatsky wrote:
[..]
> On (12/07/17 13:52), Gopi Sai Teja wrote:
> > If the length of the compressed page is greater than 75% of the PAGE_SIZE,
> > then the page is stored uncompressed in zram space. Zram space utilization
> > is improved if the threshold is 80%(5 compressed pages can be stored in
> > 4 pages).
> > 
> > If the compressed length is greater than 3068 and less than 3261, pages
> > still can be stored in compressed form in zs_malloc class 3264.
> > Currently these compressed pages belong to 4096 zs malloc class.
> 
> so this makes sense. I had another idea awhile ago
> 
> lkml.kernel.org/r/1456061274-20059-2-git-send-email-sergey.senozhatsky@...il.com
> 
> in short, 3261 is good, but not as good as it possibly can be. for the
> time being, our huge-class watermark starts at 3264. but this can
> change.
> 
> 
> a side note, I think we have sort of wrong API. zsmalloc knows better which
> object is huge. and who knows, may be we will change the number of huge
> classes someday or huge-class watermark, etc. so having "hey zsmalloc, is
> this object huge or not" API seems to be better than ZRAM's enforcement
> "hey zsmalloc, this object is huge".

and yes, I think I'd like to reduce the number of huge classes
right now we store objects [3264+, 4096] in huge clases. with
this patch
	lkml.kernel.org/r/1456061274-20059-4-git-send-email-sergey.senozhatsky@...il.com

we have extra classes and smaller huge-class-range. so we store
objects [3840+, 4096] in huge classes. less huge classes - more
compressed objects; more compressed objects - lower memory usage.

	-ss