linux-kernel - Re: [PATCH v10 09/10] mm: stop zeroing memory during allocation in vmemmap

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Message-ID: <20171006122518.y22rzeq7riyjbrbg@dhcp22.suse.cz>
Date:   Fri, 6 Oct 2017 14:25:18 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Pavel Tatashin' <pasha.tatashin@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
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Subject: Re: [PATCH v10 09/10] mm: stop zeroing memory during allocation in
 vmemmap

On Fri 06-10-17 12:11:42, David Laight wrote:
> From: Michal Hocko
> > Sent: 06 October 2017 12:47
> > On Fri 06-10-17 11:10:14, David Laight wrote:
> > > From: Pavel Tatashin
> > > > Sent: 05 October 2017 22:11
> > > > vmemmap_alloc_block() will no longer zero the block, so zero memory
> > > > at its call sites for everything except struct pages.  Struct page memory
> > > > is zero'd by struct page initialization.
> > >
> > > It seems dangerous to change an allocator to stop zeroing memory.
> > > It is probably saver to add a new function that doesn't zero
> > > the memory and use that is the places where you don't want it
> > > to be zeroed.
> > 
> > Not sure what you mean. memblock_virt_alloc_try_nid_raw is a new
> > function which doesn't zero out...
> 
> You should probably leave vmemap_alloc_block() zeroing the memory
> so that existing alls don't have to be changed - apart from the
> ones you are explicitly optimising.

But the whole point of vmemmap_alloc_block is to allocate memmaps and
the point of this change is to cover those. This is not a generic API
that other users would depend on. 
-- 
Michal Hocko
SUSE Labs