On Tue, Apr 06, 2010 at 10:06:19AM +0800, KOSAKI Motohiro wrote: > > On Tue, Apr 06, 2010 at 09:25:36AM +0800, Li, Shaohua wrote: > > > On Sun, Apr 04, 2010 at 10:19:06PM +0800, KOSAKI Motohiro wrote: > > > > > On Fri, Apr 02, 2010 at 05:14:38PM +0800, KOSAKI Motohiro wrote: > > > > > > > > > This patch makes a lot of sense than previous. however I think <1% anon ratio > > > > > > > > > shouldn't happen anyway because file lru doesn't have reclaimable pages. > > > > > > > > > <1% seems no good reclaim rate. > > > > > > > > > > > > > > > > Oops, the above mention is wrong. sorry. only 1 page is still too big. > > > > > > > > because under streaming io workload, the number of scanning anon pages should > > > > > > > > be zero. this is very strong requirement. if not, backup operation will makes > > > > > > > > a lot of swapping out. > > > > > > > Sounds there is no big impact for the workload which you mentioned with the patch. > > > > > > > please see below descriptions. > > > > > > > I updated the description of the patch as fengguang suggested. > > > > > > > > > > > > Umm.. sorry, no. > > > > > > > > > > > > "one fix but introduce another one bug" is not good deal. instead, > > > > > > I'll revert the guilty commit at first as akpm mentioned. > > > > > Even we revert the commit, the patch still has its benefit, as it increases > > > > > calculation precision, right? > > > > > > > > no, you shouldn't ignore the regression case. > > > > > I don't think this is serious. In my calculation, there is only 1 page swapped out > > > for 6G anonmous memory. 1 page should haven't any performance impact. > > > > 1 anon page scanned for every N file pages scanned? > > > > Is N a _huge_ enough ratio so that the anon list will be very light scanned? > > > > Rik: here is a little background. > > The problem is, the VM are couteniously discarding no longer used file > cache. if we are scan extra anon 1 page, we will observe tons swap usage > after few days. > > please don't only think benchmark. OK the days-of-streaming-io typically happen in file servers. Suppose a file server with 16GB memory, 1GB of which is consumed by anonymous pages, others are for page cache. Assume that the exact file:anon ratio computed by the get_scan_ratio() algorithm is 1000:1. In that case percent[0]=0.1 and is rounded down to 0, which keeps the anon pages in memory for the few days. Now with Shaohua's patch, nr[0] = (262144/4096)/1000 = 0.06 will also be rounded down to 0. It only becomes >=1 when - reclaim runs into trouble and priority goes low - anon list goes huge So I guess Shaohua's patch still has reasonable "underflow" threshold :) Thanks, Fengguang > > > Under streaming IO, the current get_scan_ratio() will get a percent[0] > > that is (much) less than 1, so underflows to 0. > > > > It has the bad effect of completely disabling the scan of anon list, > > which leads to OOM in Shaohua's test case. OTOH, it also has the good > > side effect of keeping anon pages in memory and totally prevent swap > > IO. > > > > Shaohua's patch improves the computation precision by computing nr[] > > directly in get_scan_ratio(). This is good in general, however will > > enable light scan of the anon list on streaming IO. > > In such case, percent[0] should be big. I think underflowing is not point. > His test case is merely streaming io copy, why can't we drop tmpfs cached > page? his /proc/meminfo describe his machine didn't have droppable file cache. > so, big percent[1] value seems makes no sense. no? > > I'm not sure we need either below detection. I need more investigate. > 1) detect no discardable file cache > 2) detect streaming io on tmpfs (as regular file) > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>