Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: Horrible L2 cache effects from kernel compile | Date | Tue, 25 Feb 2003 22:18:09 +0000 (UTC) |
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In article <3E5BB7EE.5090301@colorfullife.com>, Manfred Spraul <manfred@colorfullife.com> wrote: > >Are you sure that this will help?
It might, under some loads.
However, I don't think it's a long-term solution, since the hashing will mean that for any reasonably spread out load you _will_ always walk all dentries.
So the long-term solution is to either use a local lookup (which we ended up doing for the page cache) _or_ to limit the number of dentries themselves some way. The latter sounds like a bad idea.
>Btw, has anyone tried to replaced the global dcache with something >local, perhaps a tree instead of d_child, and then lookup in d_child_tree?
I'd love to see somebody try. The main worry is the overhead required per directory dentry and keeping it scalable. The dentry tree _will_ be quickly populated and one common case is a few huge directories, yet at the same time for most dentries there won't be any children at all or very few of them).
Right now the "child" list is just a simple linked list, and changing that to something more complex might make it possible to get rid of the hash entirely. But increasing the size of individual dentries is a bad idea, so it would have to be something fairly smart.
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