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Subject: Re: [PATCH v13 2/7] mm: factor helpers for memory_failure_dev_pagemap
To:     =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <naoya.horiguchi@nec.com>, Shiyang Ruan <ruansy.fnst@fujitsu.com>
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        Christoph Hellwig <hch@lst.de>
References: <20220419045045.1664996-1-ruansy.fnst@fujitsu.com>
 <20220419045045.1664996-3-ruansy.fnst@fujitsu.com>
 <20220421061344.GA3607858@hori.linux.bs1.fc.nec.co.jp>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <564100f4-fb8f-e2cf-db69-495294090ba4@huawei.com>
Date:   Thu, 21 Apr 2022 16:12:40 +0800
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On 2022/4/21 14:13, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Tue, Apr 19, 2022 at 12:50:40PM +0800, Shiyang Ruan wrote:
>> memory_failure_dev_pagemap code is a bit complex before introduce RMAP
>> feature for fsdax.  So it is needed to factor some helper functions to
>> simplify these code.
>>
>> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
>> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> 
> Thanks for the refactoring.  As I commented to 0/7, the conflict with
> "mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()"
> can be trivially resolved.
> 
> Another few comment below ...
> 
>> ---
>>  mm/memory-failure.c | 157 ++++++++++++++++++++++++--------------------
>>  1 file changed, 87 insertions(+), 70 deletions(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index e3fbff5bd467..7c8c047bfdc8 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1498,6 +1498,90 @@ static int try_to_split_thp_page(struct page *page, const char *msg)
>>  	return 0;
>>  }
>>
>> +static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
>> +		struct address_space *mapping, pgoff_t index, int flags)
>> +{
>> +	struct to_kill *tk;
>> +	unsigned long size = 0;
>> +
>> +	list_for_each_entry(tk, to_kill, nd)
>> +		if (tk->size_shift)
>> +			size = max(size, 1UL << tk->size_shift);
>> +
>> +	if (size) {
>> +		/*
>> +		 * Unmap the largest mapping to avoid breaking up device-dax
>> +		 * mappings which are constant size. The actual size of the
>> +		 * mapping being torn down is communicated in siginfo, see
>> +		 * kill_proc()
>> +		 */
>> +		loff_t start = (index << PAGE_SHIFT) & ~(size - 1);
>> +
>> +		unmap_mapping_range(mapping, start, size, 0);
>> +	}
>> +
>> +	kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
>> +}
>> +
>> +static int mf_generic_kill_procs(unsigned long long pfn, int flags,
>> +		struct dev_pagemap *pgmap)
>> +{
>> +	struct page *page = pfn_to_page(pfn);
>> +	LIST_HEAD(to_kill);
>> +	dax_entry_t cookie;
>> +	int rc = 0;
>> +
>> +	/*
>> +	 * Pages instantiated by device-dax (not filesystem-dax)
>> +	 * may be compound pages.
>> +	 */
>> +	page = compound_head(page);
>> +
>> +	/*
>> +	 * Prevent the inode from being freed while we are interrogating
>> +	 * the address_space, typically this would be handled by
>> +	 * lock_page(), but dax pages do not use the page lock. This
>> +	 * also prevents changes to the mapping of this pfn until
>> +	 * poison signaling is complete.
>> +	 */
>> +	cookie = dax_lock_page(page);
>> +	if (!cookie)
>> +		return -EBUSY;
>> +
>> +	if (hwpoison_filter(page)) {
>> +		rc = -EOPNOTSUPP;
>> +		goto unlock;
>> +	}
>> +
>> +	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
>> +		/*
>> +		 * TODO: Handle HMM pages which may need coordination
>> +		 * with device-side memory.
>> +		 */
>> +		return -EBUSY;
> 
> Don't we need to go to dax_unlock_page() as the origincal code do?

I think dax_unlock_page is needed too and please remember set rc to -EBUSY before out.

> 
>> +	}
>> +
>> +	/*
>> +	 * Use this flag as an indication that the dax page has been
>> +	 * remapped UC to prevent speculative consumption of poison.
>> +	 */
>> +	SetPageHWPoison(page);
>> +
>> +	/*
>> +	 * Unlike System-RAM there is no possibility to swap in a
>> +	 * different physical page at a given virtual address, so all
>> +	 * userspace consumption of ZONE_DEVICE memory necessitates
>> +	 * SIGBUS (i.e. MF_MUST_KILL)
>> +	 */
>> +	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
>> +	collect_procs(page, &to_kill, true);
>> +
>> +	unmap_and_kill(&to_kill, pfn, page->mapping, page->index, flags);
>> +unlock:
>> +	dax_unlock_page(page, cookie);
>> +	return rc;
>> +}
>> +
>>  /*
>>   * Called from hugetlb code with hugetlb_lock held.
>>   *
>> @@ -1644,12 +1728,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>>  		struct dev_pagemap *pgmap)
>>  {
>>  	struct page *page = pfn_to_page(pfn);
>> -	unsigned long size = 0;
>> -	struct to_kill *tk;
>>  	LIST_HEAD(tokill);
> 
> Is this variable unused in this function?

There has a to_kill in mf_generic_kill_procs. So this one is unneeded. We should remove it.

> 
> Thanks,
> Naoya Horiguchi
> 

Except for the above nit, the patch looks good to me. Thanks!

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>