linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Vlastimil Babka <vbabka@suse.cz>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Rik van Riel <riel@redhat.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>,
	Rafael Aquini <aquini@redhat.com>,
	virtualization@lists.linux-foundation.org,
	Jonathan Corbet <corbet@lwn.net>,
	John Einar Reitan <john.reitan@foss.arm.com>,
	dri-devel@lists.freedesktop.org,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Gioh Kim <gi-oh.kim@profitbricks.com>
Subject: Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration
Date: Tue, 31 May 2016 09:51:47 +0200	[thread overview]
Message-ID: <bbc87219-d86d-d7a5-2a78-9f09a1549d65@suse.cz> (raw)
In-Reply-To: <20160530162523.GA18314@bbox>

On 05/30/2016 06:25 PM, Minchan Kim wrote:
>>> --- a/mm/compaction.c
>>> +++ b/mm/compaction.c
>>> @@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
>>>
>>> #ifdef CONFIG_COMPACTION
>>>
>>> +int PageMovable(struct page *page)
>>> +{
>>> +	struct address_space *mapping;
>>> +
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	if (!__PageMovable(page))
>>> +		return 0;
>>> +
>>> +	mapping = page_mapping(page);
>>> +	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
>>> +		return 1;
>>> +
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL(PageMovable);
>>> +
>>> +void __SetPageMovable(struct page *page, struct address_space *mapping)
>>> +{
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
>>> +	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
>>> +}
>>> +EXPORT_SYMBOL(__SetPageMovable);
>>> +
>>> +void __ClearPageMovable(struct page *page)
>>> +{
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	VM_BUG_ON_PAGE(!PageMovable(page), page);
>>> +	page->mapping = (void *)((unsigned long)page->mapping &
>>> +				PAGE_MAPPING_MOVABLE);
>>> +}
>>> +EXPORT_SYMBOL(__ClearPageMovable);
>>
>> The second confusing thing is that the function is named
>> __ClearPageMovable(), but what it really clears is the mapping
>> pointer,
>> which is not at all the opposite of what __SetPageMovable() does.
>>
>> I know it's explained in the documentation, but it also deserves a
>> comment here so it doesn't confuse everyone who looks at it.
>> Even better would be a less confusing name for the function, but I
>> can't offer one right now.
>
> To me, __ClearPageMovable naming is suitable for user POV.
> It effectively makes the page unmovable. The confusion is just caused
> by the implementation and I don't prefer exported API depends on the
> implementation. So I want to add just comment.
>
> I didn't add comment above the function because I don't want to export
> internal implementation to the user. I think they don't need to know it.
>
> index a7df2ae71f2a..d1d2063b4fd9 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -108,6 +108,11 @@ void __ClearPageMovable(struct page *page)
>  {
>         VM_BUG_ON_PAGE(!PageLocked(page), page);
>         VM_BUG_ON_PAGE(!PageMovable(page), page);
> +       /*
> +        * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
> +        * flag so that VM can catch up released page by driver after isolation.
> +        * With it, VM migration doesn't try to put it back.
> +        */
>         page->mapping = (void *)((unsigned long)page->mapping &
>                                 PAGE_MAPPING_MOVABLE);

OK, that's fine!

>>
>>> diff --git a/mm/util.c b/mm/util.c
>>> index 917e0e3d0f8e..b756ee36f7f0 100644
>>> --- a/mm/util.c
>>> +++ b/mm/util.c
>>> @@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
>>> 	}
>>>
>>> 	mapping = page->mapping;
>>
>> I'd probably use READ_ONCE() here to be safe. Not all callers are
>> under page lock?
>
> I don't understand. Yeah, all caller are not under page lock but at least,
> new user of movable pages should call it under page_lock.
> Yeah, I will write the rule down in document.
> In this case, what kinds of problem do you see?

After more thinking, probably none. It wouldn't prevent any extra races. 
Sorry for the noise.

  reply	other threads:[~2016-05-31  7:51 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-20 14:23 [PATCH v6 00/12] Support non-lru page migration Minchan Kim
2016-05-20 14:23 ` [PATCH v6 01/12] mm: use put_page to free page instead of putback_lru_page Minchan Kim
2016-05-20 14:23 ` [PATCH v6 02/12] mm: migrate: support non-lru movable page migration Minchan Kim
2016-05-27 14:26   ` Vlastimil Babka
2016-05-30  1:33     ` Minchan Kim
2016-05-30  9:01       ` Vlastimil Babka
2016-05-30  1:39   ` PATCH v6v2 " Minchan Kim
2016-05-30  9:36     ` Vlastimil Babka
2016-05-30 16:25       ` Minchan Kim
2016-05-31  7:51         ` Vlastimil Babka [this message]
2016-05-31  0:01     ` [PATCH v6v3 " Minchan Kim
2016-05-31  7:52       ` Vlastimil Babka
2016-05-31 23:05         ` Minchan Kim
2016-06-13  9:38       ` Anshuman Khandual
2016-06-15  2:32         ` Minchan Kim
2016-06-15  6:45           ` Anshuman Khandual
2016-06-16  0:26             ` Minchan Kim
2016-06-16  3:42               ` Anshuman Khandual
2016-06-16  5:37                 ` Minchan Kim
2016-06-27  5:51                   ` Anshuman Khandual
2016-06-28  6:39                     ` Minchan Kim
2016-06-30  5:56                       ` Anshuman Khandual
2016-06-30  6:18                         ` Minchan Kim
2016-05-20 14:23 ` [PATCH v6 03/12] mm: balloon: use general non-lru movable page feature Minchan Kim
2016-05-30 12:16   ` Vlastimil Babka
2016-05-20 14:23 ` [PATCH v6 04/12] zsmalloc: keep max_object in size_class Minchan Kim
2016-05-20 14:23 ` [PATCH v6 05/12] zsmalloc: use bit_spin_lock Minchan Kim
2016-05-20 14:23 ` [PATCH v6 06/12] zsmalloc: use accessor Minchan Kim
2016-05-20 14:23 ` [PATCH v6 07/12] zsmalloc: factor page chain functionality out Minchan Kim
2016-05-20 14:23 ` [PATCH v6 08/12] zsmalloc: introduce zspage structure Minchan Kim
2016-05-20 14:23 ` [PATCH v6 09/12] zsmalloc: separate free_zspage from putback_zspage Minchan Kim
2016-05-20 14:23 ` [PATCH v6 10/12] zsmalloc: use freeobj for index Minchan Kim
2016-05-20 14:23 ` [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim
2016-05-24  5:28   ` Sergey Senozhatsky
2016-05-24  6:28     ` Minchan Kim
2016-05-24  8:05       ` Sergey Senozhatsky
2016-05-24  8:17         ` Minchan Kim
2016-05-25  5:14       ` Minchan Kim
2016-05-25 15:23         ` Sergey Senozhatsky
2016-05-26  0:32           ` Minchan Kim
2016-05-26  0:59             ` Sergey Senozhatsky
2016-05-26  4:37               ` Minchan Kim
2016-05-26 21:50   ` [PATCH v6r2 " Minchan Kim
2016-05-20 14:23 ` [PATCH v6 12/12] zram: use __GFP_MOVABLE for memory allocation Minchan Kim

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bbc87219-d86d-d7a5-2a78-9f09a1549d65@suse.cz \
    --to=vbabka@suse.cz \
    --cc=akpm@linux-foundation.org \
    --cc=aquini@redhat.com \
    --cc=corbet@lwn.net \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=gi-oh.kim@profitbricks.com \
    --cc=hughd@google.com \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=john.reitan@foss.arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@suse.de \
    --cc=minchan@kernel.org \
    --cc=riel@redhat.com \
    --cc=sergey.senozhatsky@gmail.com \
    --cc=virtualization@lists.linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).