Rusty Russell wrote: > On Friday 30 May 2008 15:20:45 Christoph Lameter wrote: >> On Fri, 30 May 2008, Eric Dumazet wrote: >>>> +static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]); >>> area[] is not guaranteed to be aligned on anything but 4 bytes. >>> >>> If someone then needs to call cpu_alloc(8, GFP_KERNEL, 8), it might get >>> an non aligned result. >>> >>> Either you should add an __attribute__((__aligned__(PAGE_SIZE))), >>> or take into account the real address of area[] in cpu_alloc() to avoid >>> waste of up to PAGE_SIZE bytes >>> per cpu. >> I think cacheline aligning should be sufficient. People should not >> allocate large page aligned objects here. > > I vaguely recall there were issues with this in the module code. They might > be gone now, but failing to meet alignment contraints without a big warning > would suck. > > But modifying your code to consider the actual alignment is actually pretty > trivial, AFAICT. > > Cheers, > Rusty. So paraphrasing my earlier email, we should add: bitmap_find_free_area(bitmap, nbits, size, align, alignbase) so that > cacheline alignment is possible? My thinking is that if we do go to true dynamically sized cpu_alloc area then allocating PAGE_SIZE units may be both practical and worthwhile...? Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
