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Date:   Thu, 16 Apr 2020 13:37:36 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, x86@kernel.org,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Laura Abbott <labbott@redhat.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
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Subject: Re: [PATCH 10/28] mm: only allow page table mappings for built-in
 zsmalloc
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Hi Christoph,


Sorry for the late.

On Sat, Apr 11, 2020 at 09:20:52AM +0200, Christoph Hellwig wrote:
> Hi Minchan,
> 
> On Fri, Apr 10, 2020 at 04:11:36PM -0700, Minchan Kim wrote:
> > It doesn't mean we couldn't use zsmalloc as module any longer. It means
> > we couldn't use zsmalloc as module with pgtable mapping whcih was little
> > bit faster on microbenchmark in some architecutre(However, I usually temped
> > to remove it since it had several problems). However, we could still use
> > zsmalloc as module as copy way instead of pgtable mapping. Thus, if someone
> > really want to rollback the feature, they should provide reasonable reason
> > why it doesn't work for them. "A little fast" wouldn't be enough to exports
> > deep internal to the module.
> 
> do you have any data how much faster it is on arm (and does that include
> arm64 as well)?  Besides the exports which were my prime concern,

https://github.com/sjenning/zsmapbench

I need to recall the memory. IIRC, it was almost 30% faster at that time
in ARM so was not trivial at that time. However, it was story from
several years ago.

> zsmalloc with pgtable mappings also is the only user of map_kernel_range
> outside of vmalloc.c, if it really is another code base for tiny
> improvements we could mark map_kernel_range or in fact remove it entirely
> and open code it in the remaining callers.

I alsh have temped to remove it. Let me have time to revist it in this
chance.

Thanks.