Re: [patch] real-time enhanced page allocator and throttling
From: Andrew Morton <hidden>
Date: 2003-08-06 00:08:52
Also in:
lkml
Robert Love [off-list ref] wrote:
quoted
There is a very good argument for giving !SCHED_OTHER tasks> "special treatment" in the VM. Yes, there is. Attached patch is against 2.6.0-test2-mm4.
Thanks. I guess we should extend the special treatment in the page allocator and in balance_dirty_pages() we still should go and update the various bits of state and poke pdflush if needed. These changes should yield quite significant improvements in worst-case latencies for realtime tasks under some situations. I'll test them... diff -puN mm/page_alloc.c~rt-tasks-special-vm-treatment-2 mm/page_alloc.c
--- 25/mm/page_alloc.c~rt-tasks-special-vm-treatment-2 2003-08-05 16:57:51.000000000 -0700
+++ 25-akpm/mm/page_alloc.c 2003-08-05 16:58:11.000000000 -0700@@ -592,6 +592,8 @@ __alloc_pages(unsigned int gfp_mask, uns local_min = z->pages_min; if (gfp_mask & __GFP_HIGH) local_min >>= 2; + if (rt_task(p)) + local_min >>= 1; min += local_min; if (z->free_pages >= min || (!wait && z->free_pages >= z->pages_high)) {
diff -puN mm/page-writeback.c~rt-tasks-special-vm-treatment-2 mm/page-writeback.c
--- 25/mm/page-writeback.c~rt-tasks-special-vm-treatment-2 2003-08-05 16:57:51.000000000 -0700
+++ 25-akpm/mm/page-writeback.c 2003-08-05 17:02:40.000000000 -0700@@ -144,7 +144,7 @@ get_dirty_limits(struct page_state *ps, * If we're over `background_thresh' then pdflush is woken to perform some * writeout. */ -void balance_dirty_pages(struct address_space *mapping) +static void balance_dirty_pages(struct address_space *mapping) { struct page_state ps; long nr_reclaimable;
@@ -167,8 +167,9 @@ void balance_dirty_pages(struct address_ nr_reclaimable = ps.nr_dirty + ps.nr_unstable; if (nr_reclaimable + ps.nr_writeback <= dirty_thresh) break; - dirty_exceeded = 1; + if (rt_task(current)) + break; /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. * Unstable writes are a feature of certain networked
@@ -223,7 +224,7 @@ void balance_dirty_pages_ratelimited(str * Check the rate limiting. Also, we do not want to throttle real-time * tasks in balance_dirty_pages(). Period. */ - if (get_cpu_var(ratelimits)++ >= ratelimit && !rt_task(current)) { + if (get_cpu_var(ratelimits)++ >= ratelimit) { __get_cpu_var(ratelimits) = 0; put_cpu_var(ratelimits); balance_dirty_pages(mapping);
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