Messages in this thread | | | Date | Tue, 10 Aug 2010 08:05:18 +0300 | From | Pekka Enberg <> | Subject | Re: [PATCH 04/10] Use percpu buffers |
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Hi Nitin,
On 10.8.2010 7.47, Nitin Gupta wrote: > On 08/10/2010 12:27 AM, Pekka Enberg wrote: >> On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta<ngupta@vflare.org> wrote: >>> @@ -303,38 +307,41 @@ static int zram_write(struct zram *zram, struct bio *bio) >>> zram_test_flag(zram, index, ZRAM_ZERO)) >>> zram_free_page(zram, index); >>> >>> - mutex_lock(&zram->lock); >>> + preempt_disable(); >>> + zbuffer = __get_cpu_var(compress_buffer); >>> + zworkmem = __get_cpu_var(compress_workmem); >>> + if (unlikely(!zbuffer || !zworkmem)) { >>> + preempt_enable(); >>> + goto out; >>> + } >> The per-CPU buffer thing with this preempt_disable() trickery looks >> overkill to me. Most block device drivers seem to use mempool_alloc() >> for this sort of thing. Is there some reason you can't use that here? >> > Other block drivers are allocating relatively small structs using > mempool_alloc(). However, in case of zram, these buffers are quite > large (compress_workmem is 64K!). So, allocating them on every write > would probably be much slower than using a pre-allocated per-cpu buffer. The mempool API is precisely for that - using pre-allocated buffers instead of allocating every time. The preempt_disable() games make the code complex and have the downside of higher scheduling latencies so why not give mempools a try?
Pekka
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