On Thu, 2 Sep 2010 10:28:29 +0200 Michal Hocko <mhocko@xxxxxxx> wrote: > On Thu 02-09-10 14:45:00, KAMEZAWA Hiroyuki wrote: > > On Wed, 1 Sep 2010 14:41:38 +0200 > [...] > > > From de85f1aa42115678d3340f0448cd798577036496 Mon Sep 17 00:00:00 2001 > > > From: Michal Hocko <mhocko@xxxxxxx> > > > Date: Fri, 20 Aug 2010 15:39:16 +0200 > > > Subject: [PATCH] Make is_mem_section_removable more conformable with offlining code > > > > > > Currently is_mem_section_removable checks whether each pageblock from > > > the given pfn range is of MIGRATE_MOVABLE type or if it is free. If both > > > are false then the range is considered non removable. > > > > > > On the other hand, offlining code (more specifically > > > set_migratetype_isolate) doesn't care whether a page is free and instead > > > it just checks the migrate type of the page and whether the page's zone > > > is movable. > > > > > > This can lead into a situation when we can mark a node as not removable > > > just because a pageblock is MIGRATE_RESERVE and it is not free. > > > > > > Let's make a common helper is_page_removable which unifies both tests > > > at one place. Also let's check for MIGRATE_UNMOVABLE rather than all > > > possible MIGRATEable types. > > > > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > > > > Hmm..Why MIGRATE_RECLAIMABLE is included ? > > AFAIU the code, MIGRATE_RECLAIMABLE are movable as well (at least that > is how I interpret #define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)). > Why should we prevent from memory offlining if we have some reclaimable > pages? Or am I totally misinterpreting the meaning of this flag? > RECLAIMABLE cannot be 100% reclaimable. Then, for memory hotlug, I intentionally skips it and check free_area[] and LRU. > > > > If MIGRATE_RCLAIMABLE is included, set_migrate_type() should check the > > range of pages. Because it makes the pageblock as MIGRAGE_MOVABLE after > > failure of memory hotplug. > > > > Original code checks. > > > > - the range is MIGRAGE_MOVABLE or > > - the range includes only free pages and LRU pages. > > > > Then, moving them back to MIGRAGE_MOVABLE after failure was correct. > > Doesn't this makes changes MIGRATE_RECALIMABLE to be MIGRATE_MOVABLE and > > leads us to more fragmentated situation ? > > Just to be sure that I understand you concern. We are talking about hot > remove failure which can lead to higher fragmentation, right? > right. > By the higher fragmentation you mean that all movable pageblocks (even > reclaimable) gets to MIGRATE_MOVABLE until we get first failure. In the > worst case, if we fail near the end of the zone then there is imbalance > in MIGRATE_MOVABLE vs. MIGRATE_RECALIMABLE. Is that what you are > thinking of? Doesn't this just gets the zone to the state after > onlining? Or is the problem if we fail somewhere in the middle? > No. My concern is pageblock type changes before/after memory hotplug failure. before isolation: MIGRATE_RECLAIMABLE after isolation failure : MIGRATE_MOVABLE Then, the section which was RECALAIMABLE (but caused memory hotplug failure) turns to be MIGRATE_MOVABLE and will continue to cause memory hotplug failure. (Because it contains unreclaimable(still-in-use) slab.) That means memory-hotplug success-rate goes down because of not-important check, and (your) customer believe "memory hotplug never works well hahaha." The old code checks RECLAIMABLE pageblock only contains free pages or LRU pages, In that meaning, MIGRATE_MOVABLE check itself should be removed. It's my fault. Thanks, -Kame -- 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>