Date: Thu, 12 Apr 2001 10:30:41 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Rik van Riel <riel@conectiva.com.br> Cc: David Xu <bsddiy@21cn.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: vm balance Message-ID: <200104121730.f3CHUf419830@earth.backplane.com> References: <Pine.LNX.4.21.0104121316190.18260-100000@imladris.rielhome.conectiva>
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:
:On Tue, 10 Apr 2001, Matt Dillon wrote:
:
:> It's randomness that will kill performance. You know the old saying
:> about caches: They only work if you get cache hits, otherwise
:> they only slow things down.
:
:I wonder ... how does FreeBSD handle negative directory entries?
:
:That is, /bin/sh looks through the PATH to search for some executable
:(eg grep) and doesn't find it in the first 3 directories.
:
:Does the vfs cache handle this or does FreeBSD have to go down into
:the filesystem code every time?
:
:Rik
The namei cache stores negative hits. /usr/src/sys/kern/vfs_cache.c
cache_lookup() - if ncp->nc_vp (the vnode) is NULL, the cache entry
represents a negative hit. cache_enter() - vp may be passed as NULL
to create a negative cache entry. ufs/ufs/ufs_lookup.c, calls to
cache_enter() enters positive or negative lookups as appropriate.
-Matt
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