On Fri, 25 Jul 2014 15:23:42 -0700, Arlie Stephens said: > If you want an annoying problem, explain and/or fix directory > performance on ext4. I've got a server where an ls of a directory took > 5 seconds, according to "time", even though it only has 295 entries at > present. I don't suppose you could get a trace of where that ls is spending its time with the kernel's trace facilities, or even just getting a stack trace of where that ls is in the kernel? I'll go out on a limb and ask if a *second* ls of the same directory runs quickly because it's now cache-hot. If so, I'd start looking at whether there's large amounts of *other* disk activity going on, and the reads of the directory are getting hung in the I/O queue behind other disk read/writes. Also, are you doing an 'ls' (which just requires reading the name/inode# pairs), or an 'ls -l' whihc in addition requires a stat() call to read in the inode itself)? That makes a lot of difference. Cache-cold on my laptop, and a *huge* Mail/linux-kernel directory (yes, it really *is* an 11M directory, it's got a half-million entries in it): [~] echo 3 >| /proc/sys/vm/drop_caches [~] cd Mail [~/Mail] time ls linux-kernel/ | wc -l 478401 real 0m2.387s user 0m0.500s sys 0m0.433s [~/Mail] ls -ld linux-kernel/ drwxr-xr-x. 2 valdis valdis 11005952 Jul 25 19:30 linux-kernel/ [~/Mail] time ls -l linux-kernel/ | wc -l 478402 real 0m32.915s user 0m2.483s sys 0m20.787s
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