On Tue, Apr 06, 2010 at 10:58:43AM +0800, KOSAKI Motohiro wrote: > > 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 :) > > Again, I didn't said his patch is no worth. I only said we don't have to > ignore the downside. Right, we should document both the upside and downside. The main difference happens when file:anon scan ratio > 100:1. For the current percent[] based computing, percent[0]=0 hence nr[0]=0 which disables anon list scan unconditionally, for good or for bad. For the direct nr[] computing, - nr[0] will be 0 for typical file servers, because with priority=12 and anon lru size < 1.6GB, nr[0] = (anon_size/4096)/100 < 0 - nr[0] will be non-zero when priority=1 and anon_size > 100 pages, this stops OOM for Shaohua's test case, however may not be enough to guarantee safety (your previous reverting patch can provide this guarantee). I liked Shaohua's patch a lot -- it adapts well to both the file-server case and the mostly-anon-pages case :) Thanks, Fengguang -- 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>