On Tue, Aug 12, 2014 at 05:28:52AM -0700, Eric Dumazet wrote: > On Tue, 2014-08-12 at 09:07 +0300, Kirill A. Shutemov wrote: > > On Tue, Aug 12, 2014 at 08:00:54AM +0300, Oren Twaig wrote: > > >If not, is there any fast way to change this behavior ? Maybe by > > >changing the granularity/alignment of such allocations to allow such > > >mapping ? > > > > What's the point to use vmalloc() in this case? > > Look at various large hashes we have in the system, all using > vmalloc() : > > [ 0.006856] Dentry cache hash table entries: 16777216 (order: 15, 134217728 bytes) > [ 0.033130] Inode-cache hash table entries: 8388608 (order: 14, 67108864 bytes) > [ 1.197621] TCP established hash table entries: 524288 (order: 11, 8388608 bytes) I see lower-order allocation in upstream code. Is it some distribution tweak? > I would imagine a performance difference if we were using hugepages. Okay, it's *probably* a valid point. The hash tables are only allocated with vmalloc() on NUMA system, if hashdist=1 (default on NUMA). It does it to distribute memory between nodes. vmalloc() in NUMA_NO_NODE case will allocate all memory with 0-order page allocations: no physical contiguous memory for hugepage mappings. I guess we could teach vmalloc() to interleave between nodes on PMD_SIZE chunks rather then on PAGE_SIZE if caller asks for big memory allocations. Although, I'm not sure it it would fit all vmalloc() users. We also would need to allocate PMD_SIZE-aligned virtual address range to be able to mapped allocated memory with pmds. It's *potentially* interesting research project. Any volunteers? -- Kirill A. Shutemov -- 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>