On Sat, Apr 10, 2010 at 05:20:57AM +0800, Andrew Morton wrote: > On Fri, 9 Apr 2010 14:51:04 +0800 > Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > get_scan_ratio() calculates percentage and if the percentage is < 1%, it will > > round percentage down to 0% and cause we completely ignore scanning anon/file > > pages to reclaim memory even the total anon/file pages are very big. > > > > To avoid underflow, we don't use percentage, instead we directly calculate > > how many pages should be scaned. In this way, we should get several scanned pages > > for < 1% percent. > > > > This has some benefits: > > 1. increase our calculation precision > > 2. making our scan more smoothly. Without this, if percent[x] is underflow, > > shrink_zone() doesn't scan any pages and suddenly it scans all pages when priority > > is zero. With this, even priority isn't zero, shrink_zone() gets chance to scan > > some pages. > > > > Note, this patch doesn't really change logics, but just increase precision. For > > system with a lot of memory, this might slightly changes behavior. For example, > > in a sequential file read workload, without the patch, we don't swap any anon > > pages. With it, if anon memory size is bigger than 16G, we will see one anon page > > swapped. The 16G is calculated as PAGE_SIZE * priority(4096) * (fp/ap). fp/ap > > is assumed to be 1024 which is common in this workload. So the impact sounds not > > a big deal. > > I grabbed this. > > Did we decide that this needed to be backported into 2.6.33.x? If so, > some words explaining the reasoning would be needed. > > Come to that, it's not obvious that we need this in 2.6.34 either. Not needed. > is the user-visible impact here? Should be very small I think. Thanks, Shaohua -- 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>