Messages in this thread | | | Date | Mon, 2 May 2011 21:49:54 +0800 | From | Wu Fengguang <> | Subject | Re: [RFC][PATCH] mm: cut down __GFP_NORETRY page allocation failures |
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On Mon, May 02, 2011 at 09:29:58PM +0800, Wu Fengguang wrote: > > > + if (preferred_zone && > > > + zone_watermark_ok_safe(preferred_zone, sc->order, > > > + high_wmark_pages(preferred_zone), > > > + zone_idx(preferred_zone), 0)) > > > + goto out; > > > + } > > > > As I said, I think direct reclaim path sould be fast if possbile and > > it should not a function of min_free_kbytes. > > It can be made not a function of min_free_kbytes by simply changing > high_wmark_pages() to low_wmark_pages() in the above chunk, since > direct reclaim is triggered when ALLOC_WMARK_LOW cannot be satisfied, > ie. it just dropped below low_wmark_pages(). > > But still, it costs 62ms reclaim latency (base kernel is 29ms).
I got new findings: the CPU schedule delays are much larger than reclaim delays. It does make the "direct reclaim until low watermark OK" latency less a problem :)
1000 dd test case: RECLAIM delay CPU delay nr_alloc_fail CAL (last CPU) base kernel 29ms 244ms 14586 218440 patched 62ms 215ms 5004 325
Thanks, Fengguang
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