Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap read fails

From: Alistair Popple <apopple@nvidia.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: akpm@linux-foundation.org, willy@infradead.org, vbabka@suse.cz,
	dhowells@redhat.com, neilb@suse.de, david@redhat.com,
	surenb@google.com, minchan@kernel.org, peterx@redhat.com,
	sfr@canb.auug.org.au, rcampbell@nvidia.com,
	naoya.horiguchi@nec.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap read fails
Date: Wed, 20 Apr 2022 10:25:02 +1000	[thread overview]
Message-ID: <87k0bkk2rp.fsf@nvdebian.thelocal> (raw)
In-Reply-To: <e320fb01-7d53-668e-53b5-463312ae0909@huawei.com>

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Miaohe Lin <linmiaohe@huawei.com> writes:

> On 2022/4/19 15:53, Alistair Popple wrote:
>> Also in madvise_free_pte_range() you could just remove the swap entry as it's no
>> longer needed.
>>
>
> This swap entry will be removed in madvise_dontneed_single_vma().
> And in madvise_free_pte_range(), we may need to keep it as same as
> hwpoison entry. Or am I supposed to remove it even if hwpoison entry
> is reused later?

Why would we need to keep it for MADV_FREE though? It only works on private
anonymous memory, and once the MADV_FREE operation has succeeded callers can
expect they might get zero-fill pages if accessing the memory again. Therefore
it should be safe to delete the entry. I think that applies equally to a
hwpoison entry too - there's no reason to kill the process if it has called
MADV_FREE on the range.

>
> Thanks!
>
>> Alistair Popple <apopple@nvidia.com> writes:
>>
>>> Miaohe Lin <linmiaohe@huawei.com> writes:
>>>
> ...