linux-kernel - Re: [PATCH 5/8] migrate_pages: batch _unmap and

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Date:   Tue, 03 Jan 2023 07:29:42 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Bharata B Rao <bharata@....com>,
        Alistair Popple <apopple@...dia.com>,
        haoxin <xhao@...ux.alibaba.com>
Subject: Re: [PATCH 5/8] migrate_pages: batch _unmap and _move

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Tue, 27 Dec 2022 08:28:56 +0800 Huang Ying <ying.huang@...el.com> wrote:
>
>> In this patch the _unmap and _move stage of the folio migration is
>> batched.  That for, previously, it is,
>> 
>>   for each folio
>>     _unmap()
>>     _move()
>> 
>> Now, it is,
>> 
>>   for each folio
>>     _unmap()
>>   for each folio
>>     _move()
>> 
>> Based on this, we can batch the TLB flushing and use some hardware
>> accelerator to copy folios between batched _unmap and batched _move
>> stages.
>> 
>> ...
>>
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1027,8 +1027,32 @@ static void __migrate_folio_extract(struct folio *dst,
>>  	dst->private = NULL;
>>  }
>>  
>> +static void migrate_folio_undo_src(struct folio *src,
>> +				   int page_was_mapped,
>> +				   struct anon_vma *anon_vma,
>> +				   struct list_head *ret)
>> +{
>> +	if (page_was_mapped)
>> +		remove_migration_ptes(src, src, false);
>> +	if (anon_vma)
>> +		put_anon_vma(anon_vma);
>> +	folio_unlock(src);
>> +	list_move_tail(&src->lru, ret);
>> +}
>> +
>> +static void migrate_folio_undo_dst(struct folio *dst,
>> +				   free_page_t put_new_page,
>> +				   unsigned long private)
>> +{
>> +	folio_unlock(dst);
>> +	if (put_new_page)
>> +		put_new_page(&dst->page, private);
>> +	else
>> +		folio_put(dst);
>> +}
>
> What do the above do?  Are they so obvious that no comments are needed?

Thank you for reminding, will add comments.

>
>>  static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
>> -				int force, enum migrate_mode mode)
>> +				 int force, bool force_lock, enum migrate_mode mode)
>>  {
>>  	int rc = -EAGAIN;
>>  	int page_was_mapped = 0;
>> @@ -1055,6 +1079,11 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
>>  		if (current->flags & PF_MEMALLOC)
>>  			goto out;
>>  
>> +		if (!force_lock) {
>> +			rc = -EDEADLOCK;
>> +			goto out;
>> +		}
>
> Please document the use of EDEADLOCK in this code.  What does it signify?

Sure.  Will do that in the next version.

Best Regards,
Huang, Ying

>>  		folio_lock(src);
>>  	}
>>