Re: [PATCH 30/45] vmscan: lumpy pageout

[Nikita Danilov <danilov@gmail.com>]

2009/10/7 Wu Fengguang <fengguang.wu@intel.com>:
> On Wed, Oct 07, 2009 at 06:38:37PM +0800, Nikita Danilov wrote:
>> Hello,
>>

[...]

>
> Glad to know about your experiences :) Interestingly I started with
> ->writepage() and then switch to ->writepages() because filesystems
> behave better with the latter (i.e. less file fragmentation).

By the way, why is your patch doing

        ->writepage(page->index);
        generic_writepages(page->index + 1, LUMPY_PAGEOUT_PAGES - 1);

instead of

        generic_writepages(page->index, LUMPY_PAGEOUT_PAGES);

? Is this because of the difficulties with passing back page specific
errors from generic_writepages()?

>
> I'd like to just ignore the shmem case, by adding a
> bdi_cap_writeback_dirty() check. Because clustered writing to swap
> device may be a less gain.

Or you can just call try_to_unmap() from shmem_writepage() when
wbc->for_reclaim is true.

>
> Page filtering should also be possible in write_cache_pages().  But
> what do you mean by "hard-to-fix races against inode reclamation"?

vmscan.c pageout path doesn't take a reference on inode, so the
instant ->writepage() releases lock on the page, the inode can be
freed.

>
> Thanks,
> Fengguang
>

Thank you,
Nikita.
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