Re: [PATCH] kswapd shall not sleep during page shortage

[Andrew Morton <akpm@osdl.org>]

Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> Back to arguing in favour of my patch - it seemed to me that kswapd could 
>  go to sleep leaving allocators which can't reclaim pages themselves in a 
>  bad situation. 

Yes, but those processes would be sleeping in blk_congestion_wait() during,
say, a GFP_NOIO/GFP_NOFS allocation attempt.  And in that case, they may be
holding locks whcih prevent kswapd from being able to do any work either.

>  It would have to be waken up by another instance of alloc_pages to then 
>  execute and start doing its job, while if it was executing already (madly 
>  scanning as you say), the chance it would find freeable pages quite
>  earlier.
> 
>  Note that not only disk IO can cause pages to become freeable. A user
>  can give up its reference on pagecache page for example (leaving
>  the page on LRU to be found and freed by kswapd).

yup.  Or munlock(), or direct-io completion.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>