On 03/26/19 at 03:03pm, Michal Hocko wrote: > On Tue 26-03-19 21:45:22, Baoquan He wrote: > > On 03/26/19 at 11:17am, Michal Hocko wrote: > > > On Tue 26-03-19 18:08:17, Baoquan He wrote: > > > > On 03/26/19 at 10:29am, Michal Hocko wrote: > > > > > On Tue 26-03-19 17:02:25, Baoquan He wrote: > > > > > > Reorder the allocation of usemap and memmap since usemap allocation > > > > > > is much simpler and easier. Otherwise hard work is done to make > > > > > > memmap ready, then have to rollback just because of usemap allocation > > > > > > failure. > > > > > > > > > > Is this really worth it? I can see that !VMEMMAP is doing memmap size > > > > > allocation which would be 2MB aka costly allocation but we do not do > > > > > __GFP_RETRY_MAYFAIL so the allocator backs off early. > > > > > > > > In !VMEMMAP case, it truly does simple allocation directly. surely > > > > usemap which size is 32 is smaller. So it doesn't matter that much who's > > > > ahead or who's behind. However, this benefit a little in VMEMMAP case. > > > > > > How does it help there? The failure should be even much less probable > > > there because we simply fall back to a small 4kB pages and those > > > essentially never fail. > > > > OK, I am fine to drop it. Or only put the section existence checking > > earlier to avoid unnecessary usemap/memmap allocation? > > DO you have any data on how often that happens? Should basically never > happening, right? Oh, you think about it in this aspect. Yes, it rarely happens. Always allocating firstly can increase efficiency. Then I will just drop it.
