Messages in this thread | | | Subject | Re: [RFC PATCH 1/2] Shrink compat_ioctl.c | From | Matt Mackall <> | Date | Mon, 29 Sep 2008 18:38:02 -0500 |
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On Tue, 2008-09-30 at 01:38 +0200, Andi Kleen wrote: > On Mon, Sep 29, 2008 at 06:27:10PM -0500, Matt Mackall wrote: > > I'm throwing this out untested as I don't have a mixed 64/32 system > > handy at the moment. > > Makes sense (assuming it works, haven't tested) > > > compat_ioctl: shrink structures > > > > Initially, compat_ioctl.c has a ~18k table of translated ioctls. > > Each table entry is 24 bytes but we can shrink this to 16: > > > > - use short table indexes rather than a pointer for .next values > > - use unsigned ints for cmd numbers (they're 32-bit ioctls, after all) > > > > In addition, there's a 2k hash table that we can do away with simply > > by hashifying the main table in place at init time. > > You mean by using a closed hash?
The original hash table was 256 pointers into the main table. I simply rearrange the main table so the first 256 entries have an appropriate hash. Basically:
for i in len(table): h = hash(table[i]) swap(table[i], table[hash])
At the end of this loop, table[0:256] will contain an appropriate table entry, if it exists. So no secondary table is needed.
-- Mathematics is the supreme nostalgia of our time.
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