On Tue, Oct 25, 2011 at 10:59:40AM +0800, Shaohua Li wrote: > With current logic, if page reclaim finds a huge page, it will just reclaim > the head page and leave tail pages reclaimed later. Let's take an example, > lru list has page A and B, page A is huge page: > 1. page A is isolated > 2. page B is isolated > 3. shrink_page_list() adds page A to swap page cache. so page A is split. > page A+1, page A+2, ... are added to lru list. > 4. shrink_page_list() adds page B to swap page cache. > 5. page A and B is written out and reclaimed. > 6. page A+1, A+2 ... is isolated and reclaimed later. > So the reclaim order is A, B, ...(maybe other pages), A+1, A+2 ... I don't see your code yet but have a question. You mitigate this problem by 4/5 which could add subpages into lru tail so subpages would reclaim next interation of reclaim. What do we need 5/5? Do I miss something? > > We expected the whole huge page A is reclaimed in the meantime, so > the order is A, A+1, ... A+HPAGE_PMD_NR-1, B, .... > > With this patch, we do huge page split just after the head page is isolated > for inactive lru list, so the tail pages will be reclaimed immediately. > > In a test, a range of anonymous memory is written and will trigger swap. > Without the patch: > #cat /proc/vmstat|grep thp > thp_fault_alloc 451 > thp_fault_fallback 0 > thp_collapse_alloc 0 > thp_collapse_alloc_failed 0 > thp_split 238 > > With the patch: > #cat /proc/vmstat|grep thp > thp_fault_alloc 450 > thp_fault_fallback 1 > thp_collapse_alloc 0 > thp_collapse_alloc_failed 0 > thp_split 103 > > So the thp_split number is reduced a lot, though there is one extra > thp_fault_fallback. Wow. The result seems to be good. Is it result of effect only 5/5? or both 4/5 and 5/5? -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>