On Thursday 05 June 2008 01:30:23 Mike Travis wrote: > 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 Well, my thinking is that unless we do true dynamic per-cpu, this entire patch series is a non-starter :( Once we have that, we can reopen this. Then we'll discuss why we're writing a new allocator rather than using the existing one :) Cheers, Rusty. -- 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
