On Mon, Jul 18, 2016 at 11:12:51AM +0200, Vlastimil Babka wrote: > On 07/06/2016 07:09 AM, Joonsoo Kim wrote: > >On Fri, Jun 24, 2016 at 11:54:29AM +0200, Vlastimil Babka wrote: > >>A recent patch has added whole_zone flag that compaction sets when scanning > >>starts from the zone boundary, in order to report that zone has been fully > >>scanned in one attempt. For allocations that want to try really hard or cannot > >>fail, we will want to introduce a mode where scanning whole zone is guaranteed > >>regardless of the cached positions. > >> > >>This patch reuses the whole_zone flag in a way that if it's already passed true > >>to compaction, the cached scanner positions are ignored. Employing this flag > > > >Okay. But, please don't reset cached scanner position even if whole_zone > >flag is set. Just set cc->migrate_pfn and free_pfn, appropriately. With > > Won't that result in confusion on cached position updates during > compaction where it checks the previous cached position? I wonder > what kinds of corner cases it can bring... whole_zone would come along with ignore_skip_hint so I think that there is no problem on cached position updating. > > >your following patches, whole_zone could be set without any compaction > >try > > I don't understand what you mean here? Even after whole series, > whole_zone is only checked, and positions thus reset, after passing > the compaction_suitable() call from compact_zone(). So at that point > we can say that compaction is being actually tried and it's not a > drive-by reset? My point is that we should not initialize zone's cached pfn in case of the whole_zone because what compaction with COMPACT_PRIO_SYNC_FULL want is just to scan whole range. zone's cached pfn exists for efficiency and there is no reason to initialize it by compaction with COMPACT_PRIO_SYNC_FULL. If there are some parallel compaction users, they could be benefit from un-initialized zone's cached pfn so I'd like to leave them. Thanks. -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>