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

[Lenky Gao <lenky.gao@gmail.com>]

On Thu, Mar 14, 2013 at 6:14 PM, Michal Hocko <mhocko@suse.cz> wrote:
> One way would be to increase /proc/sys/vm/min_free_kbytes which will
> enlarge watermaks so the reclaim starts sooner.
>

Good tip thanks. :)

> This is really an old kernel and also a distribution one which might
> contain a lot of patches on top of the core kernel. I would suggest to
> contact Redhat or try to reproduce the issue with the vanilla and
> up-to-date kernel and report here.

I have tested on other version vanilla kernel, such as 2.6.30 and 3.6.11, the
issue also exist and it is easy to reproduce.

Maybe i have found the answer for this question:

On Thu, Mar 14, 2013 at 4:00 PM, Lenky Gao <lenky.gao@gmail.com> wrote:
> Hi Everyone,
>
> Maybe i have found the answer for this question. The author of the JBD
> have explained in the comments:
>
> /*
>  * When an ext3-ordered file is truncated, it is possible that many pages are
>  * not successfully freed, because they are attached to a committing
> transaction.
>  * After the transaction commits, these pages are left on the LRU, with no
>  * ->mapping, and with attached buffers.  These pages are trivially reclaimable
>  * by the VM, but their apparent absence upsets the VM accounting, and it makes
>  * the numbers in /proc/meminfo look odd.
> ...
>  */
> static void release_buffer_page(struct buffer_head *bh)
> {
>         struct page *page;
> ...

But my new question is why not free those pages directly after the
transaction commits?

On Thu, Mar 14, 2013 at 8:39 PM, Hillf Danton <dhillf@gmail.com> wrote:
> Perhaps we have to consider page count for orphan page if it
> could be reproduced with mainline.
>
> 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;
>  }
>
>  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) {
>                 /*

Thanks, i'll test it.

I am totally a newbie regarding VMM and EXT/JBD, thanks to everyone
for your kind attention and help.

-- 
Regards,

Lenky

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