[issue884] Performance/memory problems under filesystem IO load

Simon 'corecode' Schubert corecode at fs.ei.tum.de
Wed Dec 19 05:01:11 PST 2007

Nicolas Thery wrote:
> Oops.  I've just noticed that block size is 4096k in the original post
> and not 4096.  I did all my experiments with the latter (there is a
> paste bug in my previous email).

I can confirm that creating a 4MB file consumes 1026 wired pages.

So either this is a) insane b) a bug or c) a counting issue, where the
buffer cache gets placed with the wired pages.

>> I traced this with gdb.  The additional wired page is part of a struct
>> buf (b_xio) instance tied to the ./file vnode.   I reckon this vnode
>> stays cached (namecache?) when the dd process ends and deleting ./file
>> forces destruction of the vnode.

I didn't yet look at the code, but does this mean that additionally to
the buffer cache data, this b_xio is kept as well, keeping the *same* data?


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