linux-kernel - Re: [PATCH 10/28] mm: only allow page table mappings for built-in zsmalloc

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Message-ID: <20200410023845.GA2354@jagdpanzerIV.localdomain>
Date:   Fri, 10 Apr 2020 11:38:45 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, x86@...nel.org,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Nitin Gupta <ngupta@...are.org>,
        Robin Murphy <robin.murphy@....com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org, linux-hyperv@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        sergey.senozhatsky@...il.com
Subject: Re: [PATCH 10/28] mm: only allow page table mappings for built-in
 zsmalloc

On (20/04/09 10:08), Minchan Kim wrote:
> > > Even though I don't know how many usecase we have using zsmalloc as
> > > module(I heard only once by dumb reason), it could affect existing
> > > users. Thus, please include concrete explanation in the patch to
> > > justify when the complain occurs.
> > 
> > The justification is 'we can unexport functions that have no sane reason
> > of being exported in the first place'.
> > 
> > The Changelog pretty much says that.
> 
> Okay, I hope there is no affected user since this patch.
> If there are someone, they need to provide sane reason why they want
> to have zsmalloc as module.

I'm one of those who use zsmalloc as a module - mainly because I use zram
as a compressing general purpose block device, not as a swap device.
I create zram0, mkfs, mount, checkout and compile code, once done -
umount, rmmod. This reduces the number of writes to SSD. Some people use
tmpfs, but zram device(-s) can be much larger in size. That's a niche use
case and I'm not against the patch.

	-ss