On Wed, Mar 18, 2015 at 03:31:00PM -0700, Andrew Morton wrote: > On Tue, 17 Mar 2015 14:09:39 -0700 Shaohua Li <shli@xxxxxx> wrote: > > > There was a similar patch posted before, but it doesn't get merged. I'd like > > to try again if there are more discussions. > > http://marc.info/?l=linux-mm&m=141230769431688&w=2 > > > > mremap can be used to accelerate realloc. The problem is mremap will > > punch a hole in original VMA, which makes specific memory allocator > > unable to utilize it. Jemalloc is an example. It manages memory in 4M > > chunks. mremap a range of the chunk will punch a hole, which other > > mmap() syscall can fill into. The 4M chunk is then fragmented, jemalloc > > can't handle it. > > Daniel's changelog had additional details regarding the userspace > allocators' behaviour. It would be best to incorporate that into your > changelog. I'll extract some from his changelog in next post > Daniel also had microbenchmark testing results for glibc and jemalloc. > Can you please do this? I run Daniel's microbenchmark too, and not surprise the result is similar: glibc: 32.82 jemalloc: 70.35 jemalloc+mremap: 33.01 tcmalloc: 68.81 but tcmalloc doesn't support mremap currently, so I cant test it. > I'm not seeing any testing results for tcmalloc and I'm not seeing > confirmation that this patch will be useful for tcmalloc. Has anyone > tried it, or sought input from tcmalloc developers? > > > This patch adds a new flag for mremap. With it, mremap will not punch the > > hole. page tables of original vma will be zapped in the same way, but > > vma is still there. That is original vma will look like a vma without > > pagefault. Behavior of new vma isn't changed. > > > > For private vma, accessing original vma will cause > > page fault and just like the address of the vma has never been accessed. > > So for anonymous, new page/zero page will be fault in. For file mapping, > > new page will be allocated with file reading for cow, or pagefault will > > use existing page cache. > > > > For shared vma, original and new vma will map to the same file. We can > > optimize this without zaping original vma's page table in this case, but > > this patch doesn't do it yet. > > > > Since with MREMAP_NOHOLE, original vma still exists. pagefault handler > > for special vma might not able to handle pagefault for mremap'd area. > > The patch doesn't allow vmas with VM_PFNMAP|VM_MIXEDMAP flags do NOHOLE > > mremap. > > At some point (preferably an early point) we'd like a manpage update > and a cc: to linux-man@xxxxxxxxxxxxxxx please. ok, will add in next post. Thanks, Shaohua -- 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>