Re: Inactive memory keep growing and how to release it?

[Simon Jeons <simon.jeons@gmail.com>]

On 03/14/2013 08:39 PM, Hillf Danton wrote:
> On Sat, Mar 9, 2013 at 10:14 AM, Will Huck <will.huckk@gmail.com> wrote:
>> Cc experts. Hugh, Johannes,
>>
>> On 03/04/2013 08:21 PM, Lenky Gao wrote:
>>> 2013/3/4 Zlatko Calusic <zlatko.calusic@iskon.hr>:
>>>> The drop_caches mechanism doesn't free dirty page cache pages. And your
>>>> bash
>>>> script is creating a lot of dirty pages. Run it like this and see if it
>>>> helps your case:
>>>>
>>>> sync; echo 3 > /proc/sys/vm/drop_caches
>>> Thanks for your advice.
>>>
>>> The inactive memory still cannot be reclaimed after i execute the sync
>>> command:
>>>
>>> # cat /proc/meminfo | grep Inactive\(file\);
>>> Inactive(file):   882824 kB
>>> # sync;
>>> # echo 3 > /proc/sys/vm/drop_caches
>>> # cat /proc/meminfo | grep Inactive\(file\);
>>> Inactive(file):   777664 kB
>>>
>>> I find these page becomes orphaned in this function, but do not understand
>>> why:
>>>
>>> /*
>>>    * If truncate cannot remove the fs-private metadata from the page, the
>>> page
>>>    * becomes orphaned.  It will be left on the LRU and may even be mapped
>>> into
>>>    * user pagetables if we're racing with filemap_fault().
>>>    *
>>>    * We need to bale out if page->mapping is no longer equal to the
>>> original
>>>    * mapping.  This happens a) when the VM reclaimed the page while we
>>> waited on
>>>    * its lock, b) when a concurrent invalidate_mapping_pages got there
>>> first and
>>>    * c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
>>>    */
>>> static int
>>> truncate_complete_page(struct address_space *mapping, struct page *page)
>>> {
>>> ...
>>>
>>> My file system type is ext3, mounted with the opteion data=journal and
>>> it is easy to reproduce.
>>>
> Perhaps we have to consider page count for orphan page if it
> could be reproduced with mainline.

Why? /proc/sys/vm/drop_caches will call invalidate_mapping_pages() 
instead of truncate_complete_page().

>
> Hillf
> ---
> --- a/mm/vmscan.c	Sun Mar 10 13:36:26 2013
> +++ b/mm/vmscan.c	Thu Mar 14 20:29:40 2013
> @@ -315,14 +315,14 @@ out:
>   	return ret;
>   }
>
> -static inline int is_page_cache_freeable(struct page *page)
> +static inline int is_page_cache_freeable(struct page *page, int has_mapping)
>   {
>   	/*
>   	 * A freeable page cache page is referenced only by the caller
>   	 * that isolated the page, the page cache radix tree and
>   	 * optional buffer heads at page->private.
>   	 */
> -	return page_count(page) - page_has_private(page) == 2;
> +	return page_count(page) - page_has_private(page) == has_mapping + 1;
>   }

page count 2 is for page cache and isolator, why you check mapping 
separately?

>   static int may_write_to_queue(struct backing_dev_info *bdi,
> @@ -393,7 +393,7 @@ static pageout_t pageout(struct page *pa
>   	 * swap_backing_dev_info is bust: it doesn't reflect the
>   	 * congestion state of the swapdevs.  Easy to fix, if needed.
>   	 */
> -	if (!is_page_cache_freeable(page))
> +	if (!is_page_cache_freeable(page, mapping ? 1 : 0))
>   		return PAGE_KEEP;
>   	if (!mapping) {
>   		/*
> --
>
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