On Wed 18-11-15 10:29:33, Vlastimil Babka wrote: > The previous patch has improved swap accounting for shmem mapping, which > however made /proc/pid/smaps more expensive for shmem mappings, as we consult > the radix tree for each pte_none entry, so the overal complexity is > O(n*log(n)). > > We can reduce this significantly for mappings that cannot contain COWed pages, > because then we can either use the statistics tha shmem object itself tracks > (if the mapping contains the whole object, or the swap usage of the whole > object is zero), or use the radix tree iterator, which is much more effective > than repeated find_get_entry() calls. > > This patch therefore introduces a function shmem_swap_usage(vma) and makes > /proc/pid/smaps use it when possible. Only for writable private mappings of > shmem objects (i.e. tmpfs files) with the shmem object itself (partially) > swapped outwe have to resort to the find_get_entry() approach. Hopefully > such mappings are relatively uncommon. > > To demonstrate the diference, I have measured this on a process that creates > a 2GB mapping and dirties single pages with a stride of 2MB, and time how long > does it take to cat /proc/pid/smaps of this process 100 times. > > Private writable mapping of a /dev/shm/file (the most complex case): > > real 0m3.831s > user 0m0.180s > sys 0m3.212s > > Shared mapping of an almost full mapping of a partially swapped /dev/shm/file > (which needs to employ the radix tree iterator). > > real 0m1.351s > user 0m0.096s > sys 0m0.768s > > Same, but with /dev/shm/file not swapped (so no radix tree walk needed) > > real 0m0.935s > user 0m0.128s > sys 0m0.344s > > Private anonymous mapping: > > real 0m0.949s > user 0m0.116s > sys 0m0.348s > > The cost is now much closer to the private anonymous mapping case, unless the > shmem mapping is private and writable. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Looks good to me Acked-by: Michal Hocko <mhocko@xxxxxxxx> [...] -- Michal Hocko SUSE Labs -- 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>