linux-kernel - Re: [PATCH v3 0/4] mm/sparse: Optimize memmap allocation during sparse

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Message-ID: <20180406110557.xg2edtjgzmsdksry@node.shutemov.name>
Date:   Fri, 6 Apr 2018 14:05:57 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andrew Morton <akpm@...ux-foundation.org>, dave.hansen@...el.com
Cc:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
        pagupta@...hat.com, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v3 0/4] mm/sparse: Optimize memmap allocation during
 sparse_init()

On Thu, Apr 05, 2018 at 03:08:42PM -0700, Andrew Morton wrote:
> On Wed, 28 Feb 2018 11:26:53 +0800 Baoquan He <bhe@...hat.com> wrote:
> 
> > This is v3 post. V1 can be found here:
> > https://www.spinics.net/lists/linux-mm/msg144486.html
> > 
> > In sparse_init(), two temporary pointer arrays, usemap_map and map_map
> > are allocated with the size of NR_MEM_SECTIONS. They are used to store
> > each memory section's usemap and mem map if marked as present. In
> > 5-level paging mode, this will cost 512M memory though they will be
> > released at the end of sparse_init(). System with few memory, like
> > kdump kernel which usually only has about 256M, will fail to boot
> > because of allocation failure if CONFIG_X86_5LEVEL=y.
> > 
> > In this patchset, optimize the memmap allocation code to only use
> > usemap_map and map_map with the size of nr_present_sections. This
> > makes kdump kernel boot up with normal crashkernel='' setting when
> > CONFIG_X86_5LEVEL=y.
> 
> This patchset could do with some more review, please?

I don't really understand sparsemem good enough to comment on the
patchset.

Dave, could you review this?

-- 
 Kirill A. Shutemov