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Message-ID: <f22c9fc8-2356-46c6-ac8e-dc97328d7fcc@linux.alibaba.com>
Date: Tue, 14 May 2024 14:41:27 +0800
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Subject: Re: [PATCH RESEND v5 3/4] mm/mlock: check for THP missing the mlock
 in try_to_unmap_one()
To: Lance Yang <ioworker0@gmail.com>, akpm@linux-foundation.org
Cc: willy@infradead.org, sj@kernel.org, maskray@google.com, ziy@nvidia.com,
 ryan.roberts@arm.com, david@redhat.com, 21cnbao@gmail.com, mhocko@suse.com,
 fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com,
 xiehuan09@gmail.com, libang.li@antgroup.com, wangkefeng.wang@huawei.com,
 songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20240513074712.7608-1-ioworker0@gmail.com>
 <20240513074712.7608-4-ioworker0@gmail.com>
From: Baolin Wang <baolin.wang@linux.alibaba.com>
In-Reply-To: <20240513074712.7608-4-ioworker0@gmail.com>
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On 2024/5/13 15:47, Lance Yang wrote:
> The TTU_SPLIT_HUGE_PMD will no longer perform immediately, so we might
> encounter a PMD-mapped THP missing the mlock in the VM_LOCKED range
> during the pagewalk. It's likely necessary to mlock this THP to prevent
> it from being picked up during page reclaim.
> 
> Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Lance Yang <ioworker0@gmail.com>

IMO, this patch should be merged into patch 2, otherwise patch 2 is 
buggy. Quote the description in the 'submission patches.rst' document:

"When dividing your change into a series of patches, take special care 
to ensure that the kernel builds and runs properly after each patch in 
the series.  Developers using ``git bisect`` to track down a problem can 
end up splitting your patch series at any point; they will not thank you 
if you introduce bugs in the middle."

> ---
>   mm/rmap.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 4c4d14325f2e..08a93347f283 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1671,7 +1671,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>   		if (!(flags & TTU_IGNORE_MLOCK) &&
>   		    (vma->vm_flags & VM_LOCKED)) {
>   			/* Restore the mlock which got missed */
> -			if (!folio_test_large(folio))
> +			if (!folio_test_large(folio) ||
> +			    (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)))
>   				mlock_vma_folio(folio, vma);
>   			goto walk_done_err;
>   		}