Re: [PATCH v2] mm: page_alloc: avoid excessive IRQ disabled times in free_unref_page_list

[Andrew Morton <akpm@linux-foundation.org>]

On Fri,  8 Dec 2017 12:42:17 +0100 Lucas Stach <l.stach@pengutronix.de> wrote:

> Since 9cca35d42eb6 (mm, page_alloc: enable/disable IRQs once when freeing
> a list of pages) we see excessive IRQ disabled times of up to 25ms on an
> embedded ARM system (tracing overhead included).
> 
> This is due to graphics buffers being freed back to the system via
> release_pages(). Graphics buffers can be huge, so it's not hard to hit
> cases where the list of pages to free has 2048 entries. Disabling IRQs
> while freeing all those pages is clearly not a good idea.
> 
> Introduce a batch limit, which allows IRQ servicing once every few pages.
> The batch count is the same as used in other parts of the MM subsystem
> when dealing with IRQ disabled regions.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> v2: Try to keep the working set of pages used in the second loop cache
>     hot by going through both loops in swathes of SWAP_CLUSTER_MAX
>     entries, as suggested by Andrew Morton.
> 
>     To avoid the need to replicate the batch counting in both loops
>     I introduced a local batched_free_list where pages to be freed
>     in the critical section are collected. IMO this makes the code
>     easier to follow.

Thanks.  Is anyone motivated enough to determine whether this is
worthwhile?


--
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:"dont@kvack.org"> email@kvack.org </a>