On Mon 19-02-18 10:19:35, Mel Gorman wrote: [...] > Access to the pool is unprotected so you might create a reserve for jumbo > frames only to have them consumed by something else entirely. It's not > clear if that is even fixable as GFP flags are too coarse. > > It is not covered in the changelog why MIGRATE_HIGHATOMIC was not > sufficient for jumbo frames which are generally expected to be allocated > from atomic context. If there is a problem there then maybe > MIGRATE_HIGHATOMIC should be made more strict instead of a hack like > this. It'll be very difficult, if not impossible, for this to be tuned > properly. > > Finally, while I accept that fragmentation over time is a problem for > unmovable allocations (fragmentation protection was originally designed > for THP/hugetlbfs), this is papering over the problem. If greater > protections are needed then the right approach is to be more strict about > fallbacks. Specifically, unmovable allocations should migrate all movable > pages out of migrate_unmovable pageblocks before falling back and that > can be controlled by policy due to the overhead of migration. For atomic > allocations, allow fallback but use kcompact or a workqueue to migrate > movable pages out of migrate_unmovable pageblocks to limit fallbacks in > the future. Completely agreed! > I'm not a fan of this patch. Yes, I think the approach is just wrong. It will just hit all sorts of weird corner cases and won't work reliable for those who care. -- Michal Hocko SUSE Labs -- 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>
