Michal Hocko <mhocko@xxxxxxxxxx> writes: > On Sat 01-04-17 12:47:56, Huang, Ying wrote: >> Hi, Michal, >> >> Michal Hocko <mhocko@xxxxxxxxxx> writes: >> >> > On Fri 24-03-17 06:56:10, Dave Hansen wrote: >> >> On 03/24/2017 12:33 AM, John Hubbard wrote: >> >> > There might be some additional information you are using to come up with >> >> > that conclusion, that is not obvious to me. Any thoughts there? These >> >> > calls use the same underlying page allocator (and I thought that both >> >> > were subject to the same constraints on defragmentation, as a result of >> >> > that). So I am not seeing any way that kmalloc could possibly be a >> >> > less-fragmenting call than vmalloc. >> >> >> >> You guys are having quite a discussion over a very small point. >> >> >> >> But, Ying is right. >> >> >> >> Let's say we have a two-page data structure. vmalloc() takes two >> >> effectively random order-0 pages, probably from two different 2M pages >> >> and pins them. That "kills" two 2M pages. >> >> >> >> kmalloc(), allocating two *contiguous* pages, is very unlikely to cross >> >> a 2M boundary (it theoretically could). That means it will only "kill" >> >> the possibility of a single 2M page. More 2M pages == less fragmentation. >> > >> > Yes I agree with this. And the patch is no brainer. kvmalloc makes sure >> > to not try too hard on the kmalloc side so I really didn't get the >> > objection about direct compaction and reclaim which initially started >> > this discussion. Besides that the swapon path usually happens early >> > during the boot where we should have those larger blocks available. >> >> Could I add your Acked-by for this patch? > > Yes but please add the reasoning pointed out by Dave. As the patch > doesn't give any numbers and it would be fairly hard to add some without > artificial workloads we should at least document our current thinking > so that we can revisit it later. > > Thanks! > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks, will add the reasoning. Best Regards, Huang, Ying -- 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>
