linux-kernel - Re: [PATCH] mm/swapfile: skip HugeTLB pages for unuse

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Message-Id: <ED9675B2-C82C-45D0-861B-48828553F53D@linux.dev>
Date: Tue, 15 Oct 2024 10:33:36 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Liu Shixin <liushixin2@...wei.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Naoya Horiguchi <nao.horiguchi@...il.com>,
 linux-mm@...ck.org,
 linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH] mm/swapfile: skip HugeTLB pages for unuse_vma



> On Oct 15, 2024, at 09:45, Liu Shixin <liushixin2@...wei.com> wrote:
> 
> I got a bad pud error and lost a 1GB HugeTLB when calling swapoff.
> The problem can be reproduced by the following steps:
> 
> 1. Allocate an anonymous 1GB HugeTLB and some other anonymous memory.
> 2. Swapout the above anonymous memory.
> 3. run swapoff and we will get a bad pud error in kernel message:
> 
>  mm/pgtable-generic.c:42: bad pud 00000000743d215d(84000001400000e7)
> 
> We can tell that pud_clear_bad is called by pud_none_or_clear_bad
> in unuse_pud_range() by ftrace. And therefore the HugeTLB pages will
> never be freed because we lost it from page table. We can skip
> HugeTLB pages for unuse_vma to fix it.
> 
> Fixes: 0fe6e20b9c4c ("hugetlb, rmap: add reverse mapping for hugepage")
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>

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

Thanks.