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

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Date:   Thu, 7 Dec 2017 17:45:10 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Gopi Sai Teja <gopi.st@...sung.com>
Cc:     minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, 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 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".

	-ss