linux-kernel - Re: [PATCH mm-unstable v1] mm/hugetlb_vmemmap: don't synchronize

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Message-Id: <DE0EB84C-B69E-4FA0-8CBC-516BEB821BDE@linux.dev>
Date: Fri, 19 Jul 2024 14:18:26 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Yu Zhao <yuzhao@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Linux Memory Management List <linux-mm@...ck.org>,
 LKML <linux-kernel@...r.kernel.org>,
 kernel test robot <oliver.sang@...el.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Marc Hartmayer <mhartmay@...ux.ibm.com>
Subject: Re: [PATCH mm-unstable v1] mm/hugetlb_vmemmap: don't
 synchronize_rcu() without HVO



> On Jul 19, 2024, at 12:25, Yu Zhao <yuzhao@...gle.com> wrote:
> 
> hugetlb_vmemmap_optimize_folio() and hugetlb_vmemmap_restore_folio()
> are wrappers meant to be called regardless of whether HVO is enabled.
> Therefore, they should not call synchronize_rcu(). Otherwise, it
> regresses use cases not enabling HVO.
> 
> So move synchronize_rcu() to __hugetlb_vmemmap_optimize_folio() and
> __hugetlb_vmemmap_restore_folio(), and call it once for each batch of
> folios when HVO is enabled.
> 
> Fixes: bd225530a4c7 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202407091001.1250ad4a-oliver.sang@intel.com
> Reported-by: Janosch Frank <frankja@...ux.ibm.com>
> Tested-by: Marc Hartmayer <mhartmay@...ux.ibm.com>
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>

Acked-by: Muchun Song <muchun.song@...ux.dev>

Thanks.