Messages in this thread | | | Date | Fri, 4 Jan 2002 15:51:22 +0100 | From | Andrea Arcangeli <> | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable |
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On Fri, Jan 04, 2002 at 03:24:09PM +0100, Stephan von Krawczynski wrote: > On Fri, 4 Jan 2002 15:14:38 +0100 > Andrea Arcangeli <andrea@suse.de> wrote: > > > On Fri, Jan 04, 2002 at 01:33:21PM +0100, Stephan von Krawczynski wrote: > > > On Thu, 03 Jan 2002 20:14:42 -0600 > > > "M.H.VanLeeuwen" <vanl@megsinet.net> wrote: > > > > > > And there is another difference here: > > > > > > + if (max_mapped <= 0 && nr_pages > 0) > > > + swap_out(priority, gfp_mask, classzone); > > > + > > > > > > It sounds reasonable _not_ to swap in case of success (nr_pages == 0). > > > To me this looks pretty interesting. Is something like this already in -aa? > > > This patch may be worth applying in 2.4. It is small and looks like the > right> > thing to do. > > > > -aa swapout as soon as max_mapped hits zero. So it basically does it > > internally (i.e. way more times) and so it will most certainly be able > > to sustain an higher swap transfer rate. You can check with the mtest01 > > -w test from ltp. > > Hm, but do you think this is really good in overall performance, especially the > frequent cases where no swap should be needed _at all_ to do a successful > shrinking? And - as can be viewed in Martins tests - if you have no swap at
the common case is that max_mapped doesn't reach zero, so either ways (mainline or -aa) it's the same (i.e. no special exit path).
> all, you seem to trigger OOM earlier through the short path exit in shrink, > which is a obvious nono. I would state it wrong to fix the oom-killer for this > case, because it should not be reached at all.
Correct. Incidentally swap or no swap doesn't make any difference on the exit-path of shrink_cache in -aa (furthmore if swap is full or if everything is unfreeable I stop wasting an huge amount of time on the swap_out path at the first failure, this allows graceful oom handling or it would nearly deadlock there trying tp swap unfreeable stuff at every max_mapped reached). In -aa max_mapped doesn't influcence in any way the exit path of shrink_cache. max_mapped only controls the swapout-frequency. See:
if (!page->mapping || page_count(page) > 1) { spin_unlock(&pagecache_lock); UnlockPage(page); page_mapped: if (--max_mapped < 0) { spin_unlock(&pagemap_lru_lock);
shrink_dcache_memory(vm_scan_ratio, gfp_mask); shrink_icache_memory(vm_scan_ratio, gfp_mask); #ifdef CONFIG_QUOTA shrink_dqcache_memory(vm_scan_ratio, gfp_mask); #endif
if (!*failed_swapout) *failed_swapout = !swap_out(classzone);
max_mapped = orig_max_mapped; spin_lock(&pagemap_lru_lock); } continue; }
So it should work just fine as far I can tell.
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