Re: [PATCH] mm: cma: allocate pages from CMA if NR_FREE_PAGES approaches low water mark

On Mon, 19 Nov 2012 16:38:18 +0100
Marek Szyprowski [off-list ref] wrote:

Hello,

On 11/14/2012 11:58 PM, Andrew Morton wrote:

quoted

On Mon, 12 Nov 2012 09:59:42 +0100
Marek Szyprowski [off-list ref] wrote:

quoted

It has been observed that system tends to keep a lot of CMA free pages
even in very high memory pressure use cases. The CMA fallback for movable
pages is used very rarely, only when system is completely pruned from
MOVABLE pages, what usually means that the out-of-memory even will be
triggered very soon. To avoid such situation and make better use of CMA
pages, a heuristics is introduced which turns on CMA fallback for movable
pages when the real number of free pages (excluding CMA free pages)
approaches low water mark.

...

quoted

erk, this is right on the page allocator hotpath.  Bad.

Yes, I know that it adds an overhead to allocation hot path, but I found 
no other
place for such change. Do You have any suggestion where such change can 
be applied
to avoid additional load on hot path?

Do the work somewhere else, not on a hot path?  Somewhere on the page
reclaim path sounds appropriate.  How messy would it be to perform some
sort of balancing at reclaim time?


--
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>