Messages in this thread | | | Date | Sat, 29 Jun 2013 10:20:01 +0800 | From | Zheng Liu <> | Subject | Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting |
| |
On 06/28/2013 11:48 PM, Dave Hansen wrote: > On 06/27/2013 10:47 PM, Zheng Liu wrote: >>> I've been doing some testing involving large amounts of >>> page cache. It's quite painful to get hundreds of GB >>> of page cache mapped in, especially when I am trying to >>> do it in parallel threads. This is true even when the >>> page cache is already allocated and I only need to map >>> it in. The test: >>> >>> 1. take 160 16MB files >>> 2. clone 160 threads, mmap the 16MB files, and either >>> a. walk through the file touching each page >> >> Why not change MAP_POPULATE flag in mmap(2)? Now it is only for private >> mappings. But maybe we could let it support shared mapping. > > Adding that support to mmap() will certainly _help_ some folks. But, > anything that mmap()s something is taking mmap_sem for write. That > means that threaded apps doing mmap()/munmap() frequently are _not_ > scalable. > > IOW, a process needing to do a bunch of MAP_POPULATEs isn't > parallelizable, but one using this mechanism would be.
I look at the code, and it seems that we will handle MAP_POPULATE flag after we release mmap_sem locking in vm_mmap_pgoff():
down_write(&mm->mmap_sem); ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff, &populate); up_write(&mm->mmap_sem); if (populate) mm_populate(ret, populate);
Am I missing something?
Regards, - Zheng
| |