On Wed, Jun 20, 2012 at 9:55 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote: > On 06/21/2012 10:39 AM, KOSAKI Motohiro wrote: > >>>> number of isolate page block is almost always 0. then if we have such counter, >>>> we almost always can avoid zone->lock. Just idea. >>> >>> Yeb. I thought about it but unfortunately we can't have a counter for MIGRATE_ISOLATE. >>> Because we have to tweak in page free path for pages which are going to free later after we >>> mark pageblock type to MIGRATE_ISOLATE. >> >> I mean, >> >> if (nr_isolate_pageblock != 0) >> free_pages -= nr_isolated_free_pages(); // your counting logic >> >> return __zone_watermark_ok(z, alloc_order, mark, >> classzone_idx, alloc_flags, free_pages); >> >> >> I don't think this logic affect your race. zone_watermark_ok() is already >> racy. then new little race is no big matter. > > > It seems my explanation wasn't enough. :( > I already understand your intention but we can't make nr_isolate_pageblock. > Because we should count two type of free pages. I mean, move_freepages_block increment number of page *block*, not pages. number of free *pages* are counted by zone_watermark_ok_safe(). > 1. Already freed page so they are already in buddy list. > Of course, we can count it with return value of move_freepages_block(zone, page, MIGRATE_ISOLATE) easily. > > 2. Will be FREEed page by do_migrate_range. > It's a _PROBLEM_. For it, we should tweak free path. No? No. > If All of pages are PageLRU when hot-plug happens(ie, 2), nr_isolate_pagblock is zero and > zone_watermk_ok_safe can't do his role. number of isolate pageblock don't depend on number of free pages. It's a concept of an attribute of PFN range. -- 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/ . Don't email: <a href