On Fri, 2016-08-19 at 12:12 +0200, Michal Hocko wrote: > Hi, > this is rebased on top of next-20160818. Joe has pointed out that > meminfo is using a similar trick so I have extracted guts of what we > have already and made it more generic to be usable for smaps as well > (patch 1). The second patch then replaces seq_printf with seq_write > and show_val_kb which should have smaller overhead and my measuring (in > kvm) shows quite a nice improvements. I hope kvm is not playing tricks > on me but I didn't get to test on a real HW. Hi Michal. A few comments: For the first patch: I think this isn't worth the expansion in object size (x86-64 defconfig) $ size fs/proc/meminfo.o* text data bss dec hex filename 2698 8 0 2706 a92 fs/proc/meminfo.o.new 2142 8 0 2150 866 fs/proc/meminfo.o.old Creating a new static in task_mmu would be smaller and faster code. There are only 3 other uses of %8lu in fs/proc/task_nommu.c and those use bytes not kB. There are a few other likely not performance sensitive similar uses in <arch>/mm $ git grep -E "seq_printf.*%8lu kB" arch arch/x86/mm/pageattr.c: seq_printf(m, "DirectMap4k: %8lu kB\n", arch/x86/mm/pageattr.c: seq_printf(m, "DirectMap2M: %8lu kB\n", arch/x86/mm/pageattr.c: seq_printf(m, "DirectMap4M: %8lu kB\n", arch/x86/mm/pageattr.c: seq_printf(m, "DirectMap1G: %8lu kB\n", arch/s390/mm/pageattr.c: seq_printf(m, "DirectMap4k: %8lu kB\n", arch/s390/mm/pageattr.c: seq_printf(m, "DirectMap1M: %8lu kB\n", arch/s390/mm/pageattr.c: seq_printf(m, "DirectMap2G: %8lu kB\n", For the second patch: seq_show starts with a PAGE_SIZE buffer and if that buffer isn't big enough, seq_show redoes the entire output done to that point into a new buffer << 1 until the buffer is big enough to hold the output. So I expect this case of multiple pages / megabytes worth of smap output (40MB in your pathological case) would be rather faster if single_open_size was used appropriately for expected output size. And this would definitely be faster if seq_has_overflowed() was used somewhere in the iteration loop. -- 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>