linux-kernel - Re: [PATCH v2] mm/sparse.c: Use kvmalloc_node/kvfree to alloc/free memmap for the classic sparse

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Message-ID: <20200312135446.GK27711@MiWiFi-R3L-srv>
Date:   Thu, 12 Mar 2020 21:54:46 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        akpm@...ux-foundation.org, david@...hat.com,
        richard.weiyang@...il.com
Subject: Re: [PATCH v2] mm/sparse.c: Use kvmalloc_node/kvfree to alloc/free
 memmap for the classic sparse

On 03/12/20 at 06:34am, Matthew Wilcox wrote:
> On Thu, Mar 12, 2020 at 09:08:22PM +0800, Baoquan He wrote:
> > This change makes populate_section_memmap()/depopulate_section_memmap
> > much simpler.
> > 
> > Suggested-by: Michal Hocko <mhocko@...nel.org>
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> > v1->v2:
> >   The old version only used __get_free_pages() to replace alloc_pages()
> >   in populate_section_memmap().
> >   http://lkml.kernel.org/r/20200307084229.28251-8-bhe@redhat.com
> > 
> >  mm/sparse.c | 27 +++------------------------
> >  1 file changed, 3 insertions(+), 24 deletions(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index bf6c00a28045..362018e82e22 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -734,35 +734,14 @@ static void free_map_bootmem(struct page *memmap)
> >  struct page * __meminit populate_section_memmap(unsigned long pfn,
> >  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
> >  {
> > -	struct page *page, *ret;
> > -	unsigned long memmap_size = sizeof(struct page) * PAGES_PER_SECTION;
> > -
> > -	page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
> > -	if (page)
> > -		goto got_map_page;
> > -
> > -	ret = vmalloc(memmap_size);
> > -	if (ret)
> > -		goto got_map_ptr;
> > -
> > -	return NULL;
> > -got_map_page:
> > -	ret = (struct page *)pfn_to_kaddr(page_to_pfn(page));
> > -got_map_ptr:
> > -
> > -	return ret;
> > +	return kvmalloc_node(sizeof(struct page) * PAGES_PER_SECTION,
> > +			     GFP_KERNEL|__GFP_NOWARN, nid);
> 
> Use of NOWARN here is inappropriate, because there's no fallback.

kvmalloc_node has added __GFP_NOWARN internally when try to allocate
continuous pages. I will remove it.

> Also, I'd use array_size(sizeof(struct page), PAGES_PER_SECTION).

It's fine to me, even though we know it has no risk to overflow. I will
use array_size. Thanks.