linux-kernel - Re: [PATCH v7 3/7] mm,hugetlb: Clear HPageFreed outside of the lock

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Date:   Wed, 14 Apr 2021 09:41:32 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/7] mm,hugetlb: Clear HPageFreed outside of the lock

On Wed, Apr 14, 2021 at 08:04:21AM +0200, Michal Hocko wrote:
> On Tue 13-04-21 14:19:03, Mike Kravetz wrote:
> > On 4/13/21 6:23 AM, Michal Hocko wrote:
> > The only place where page->private may not be initialized is when we do
> > allocations at boot time from memblock.  In this case, we will add the
> > pages to the free list via put_page/free_huge_page so the appropriate
> > flags will be cleared before anyone notices.
> 
> Pages allocated by the bootmem should be pre initialized from the boot,
> no?

I guess Mike means:

hugetlb_hstate_alloc_pages
 alloc_bootmem_huge_page
  __alloc_bootmem_huge_page
   memblock_alloc_try_nid_raw

and AFAICS, memblock_alloc_try_nid_raw() does not zero the memory.

Then these pages are initialized in:

gather_bootmem_prealloc
 prep_compound_huge_page
 prep_new_huge_page

But as can be noticed, no one touches page->private when coming from that
path.

-- 
Oscar Salvador
SUSE L3