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

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Date:   Wed, 8 Apr 2020 17:36:02 +0200
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...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>,
        Minchan Kim <minchan@...nel.org>,
        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
Subject: Re: [PATCH 10/28] mm: only allow page table mappings for built-in
 zsmalloc

On Wed, Apr 08, 2020 at 08:15:19AM -0700, Matthew Wilcox wrote:
> > > >  config ZSMALLOC_PGTABLE_MAPPING
> > > >  	bool "Use page table mapping to access object in zsmalloc"
> > > > -	depends on ZSMALLOC
> > > > +	depends on ZSMALLOC=y
> > > 
> > > It's a bool so this shouldn't matter... not needed.
> > 
> > My mm/Kconfig has:
> > 
> > config ZSMALLOC
> > 	tristate "Memory allocator for compressed pages"
> > 	depends on MMU
> > 
> > which I think means it can be modular, no?
> 
> Randy means that ZSMALLOC_PGTABLE_MAPPING is a bool, so I think hch's patch
> is wrong ... if ZSMALLOC is 'm' then ZSMALLOC_PGTABLE_MAPPING would become
> 'n' instead of 'y'.

In Linus' tree you can select PGTABLE_MAPPING=y with ZSMALLOC=m,
and that fits my understanding of the kbuild language.  With this
patch I can't anymore.