Messages in this thread | | | Date | Wed, 16 Mar 2011 14:51:16 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [PATCH 5/8] mm/slub: Factor out some common code. |
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On Wed, 16 Mar 2011, George Spelvin wrote:
> > Where's your signed-off-by? > > Somewhere under the pile of crap on my desk. :-) > (More to the point, waiting for me to think it's good enough to submit > For Real.) >
Patches that you would like to propose but don't think are ready for merge should have s/PATCH/RFC/ done on the subject line.
> > Nice cleanup. > > > > "flag" should be unsigned long in all of these functions: the constants > > are declared with UL suffixes in slab.h. > > Actually, I did that deliberately. Because there's a problem I keep > wondering about, which repeats many many times in the kernel: >
You deliberately created a helper function to take an unsigned int when the actuals being passed in are all unsigned long to trigger a discussion on why they are unsigned long?
> *Why* are they unsigned long? That's an awkward type: 32 bits on many > architectures, so we can't portably assign more than 32 bits, and on > platforms where it's 64 bits, the upper 32 are just wasting space. > (And REX prefixes on x86-64.) >
unsigned long uses the native word size of the architecture which can generate more efficient code; we typically imply that flags have a limited size by including leading zeros in their definition for 32-bit compatibility:
#define SLAB_DEBUG_FREE 0x00000100UL /* DEBUG: Perform (expensive) checks on free */ #define SLAB_RED_ZONE 0x00000400UL /* DEBUG: Red zone objs in a cache */ #define SLAB_POISON 0x00000800UL /* DEBUG: Poison objects */ ...
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