Linus Torvalds wrote: > I do have another case I'm not entirely happy about - our negative > lookups (ie looking up a pathname that doesn't exist) hit in the > dcache for real filesystems and perform really well, but they suck for > tmpfs. Al, we turn off negative dentry caches for tmpfs because > simple_dentry_operations uses > > .d_delete = always_delete_dentry, > > Do we care? It's noticeable in benchmarks: it's almost an order of > magnitude difference when looking up non-existent files. I can look up > a non-existent file 23M times per second on ext4, but only 3.3M on > /tmp. I care, at least as of RHEL6 (2.6.32) kernels. Some users are using tmpfs in order to avoid dentry cache bouncing bomb (a series of simple stat() calls take about 10 seconds when there are 300,000,000+ unused dentries, P31 of http://I-love.SAKURA.ne.jp/tomoyo/LCJ2014-en.pdf ). I don't know performance on recent kernels. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
