On Tue, 2018-10-30 at 07:06 +0100, Michal Hocko wrote: > On Tue 30-10-18 09:29:10, Miles Chen wrote: > > On Mon, 2018-10-29 at 09:17 +0100, Michal Hocko wrote: > > > On Mon 29-10-18 09:07:08, Michal Hocko wrote: > > > [...] > > > > Besides that, the following doesn't make much sense to me. It simply > > > > makes no sense to use vmalloc for sub page allocation regardless of > > > > HIGHMEM. > > > > > > OK, it is still early morning here. Now I get the point of the patch. > > > You just want to (ab)use highmeme for smaller requests. I do not like > > > this, to be honest. It causes an internal fragmentation and more > > > importantly the VMALLOC space on 32b where HIGHMEM is enabled (do we > > > have any 64b with HIGHMEM btw?) is quite small to be wasted like that. > > > > > thanks for your comment. It looks like that using vmalloc fallback for > > sub page allocation is not good here. > > > > Your comment gave another idea: > > > > 1. force kbuf to PAGE_SIZE > > 2. allocate a page by alloc_page(GFP_KERNEL | __GFP_HIGHMEM); so we can > > get a highmem page if possible > > 3. use kmap/kunmap pair to create mapping for this page. No vmalloc > > space is used. > > 4. do not change kvmalloc logic. > > If you mean for this particular situation then is this really worth > it? I mean this is a short term allocation for root only so you do not > have to worry about low mem depletion. The 1...3 are applied to print_page_owner(), not in kmalloc() or kvmalloc() logic. It's a real problem when using page_owner. I found this issue recently: I'm not able to read page_owner information during a overnight test. (error: read failed: Out of memory). I replace kmalloc() with vmalloc() and it worked well. > > If you are thiking in more generic terms to allow kmalloc to use highmem > then I am not really sure this will work out. I'm thinking about modify print_page_owner().
