Messages in this thread | | | Date | Sat, 22 May 2004 01:26:02 -0700 | From | William Lee Irwin III <> | Subject | Re: slab redzoning |
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William Lee Irwin III wrote: >>-if ((size < 4096 || fls(size-1) == fls(size-1+3*BYTES_PER_WORD))) >>+if (size + 3*BYTES_PER_WORD <= PAGE_SIZE ||
On Sat, May 22, 2004 at 10:02:25AM +0200, Manfred Spraul wrote: > I understand this change: objects between 4082 and 4095 bytes are > redzoned and cause order==1 allocations, that's wrong.
William Lee Irwin III wrote: > >+ ((size & (size - 1)) && > >+ (1 << fls(size)) - size > 3*BYTES_PER_WORD))
On Sat, May 22, 2004 at 10:02:25AM +0200, Manfred Spraul wrote: > Why this change? I've tested my fls(size-1)==fls(size-1-3*4) approach > and it always returned the right result: No redzoning between 8181 and > 8192 bytes, between 16373 and 16384, etc.
It returns a false positive when size + 3*BYTES_PER_WORD == 2**n, e.g. size == 16373. Here, fls(size - 1) == 13, but fls(size - 1 + 12) == 13 while size - 1 + 12 == 16384, where we'd want the check to fail. Or so my analysis of it goes.
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