linux-kernel - Re: [patch v2 4/4] mm, mempool: poison elements backed by page allocator

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Date:	Thu, 2 Apr 2015 18:04:00 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Kleikamp <shaggy@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Catalin Marinas <catalin.marinas@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	jfs-discussion@...ts.sourceforge.net
Subject: Re: [patch v2 4/4] mm, mempool: poison elements backed by page
 allocator

On Tue, 31 Mar 2015, Andrey Ryabinin wrote:

> > We don't have a need to set PAGE_EXT_DEBUG_POISON on these pages sitting 
> > in the reserved pool, nor do we have a need to do kmap_atomic() since it's 
> > already mapped and must be mapped to be on the reserved pool, which is 
> > handled by mempool_free().
> > 
> 
> Hmm.. I just realized that this statement might be wrong.
> Why pages has to be mapped to be on reserved pool?
> mempool could be used for highmem pages and there is no need to kmap()
> until these pages will be used.
> 
> drbd (drivers/block/drbd) already uses mempool for highmem pages:
> 

Yes, you're exactly right, I didn't see this because the mempool is 
created in one file and then solely used in another file, but regardless 
we still need protection from this usecase.
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