Jens Axboe wrote:
Looks good, I've been toying with something very similar for a long time myself.
The unplug change is a no-brainer.
Yep - I may have even stolen it from you (or someone) from a patch which had been forgotten. I can't remember for sure, but it is trivial enough that anyone could come up with it if they noticed, so I won't worry about attribution ;)
The retry stuff i __make_request() will make no real difference on 'typical' hardware, when it was introduced in 2.4.x it was very useful on slower devices like dvd-rams. The batch wakeups should take care of this.
OK cool, that was the main thing I was unsure of.
The atomic-vs-blocking allocation should be tested. I'd really like it to be a "don't dive into the vm very much, just wait on the mempool" type allocation, so we are not at the mercy of long vm reclaim times hurting the latencies here.
Ahh yes I forgot it was backing it with a mempool. The problem I see with that is that GFP_ATOMIC allocations eat into the mm's "atomic reserve" pool (main use: networking), which would be nice not to.
So long as we are sure that we'll *eventually* fall back to the mempool, it should be OK (but I still agree should have testing) - that isn't entirely clear though, because the page allocator infinitely loops on small allocations unless __GFP_NORETRY is set.
Andrew - tell me I'm missing something?
---
linux-2.6-npiggin/mm/mempool.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletion(-)
diff -puN mm/mempool.c~mempool-can-fail mm/mempool.c
--- linux-2.6/mm/mempool.c~mempool-can-fail 2005-03-29 19:45:02.000000000
+1000
+++ linux-2.6-npiggin/mm/mempool.c 2005-03-29 19:48:05.000000000 +1000
@@ -198,7 +198,10 @@ void * mempool_alloc(mempool_t *pool, in
void *element;
unsigned long flags;
DEFINE_WAIT(wait);
- int gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
+ int gfp_nowait;
+
+ gfp_mask |= __GFP_NORETRY; /* don't loop in __alloc_pages */
+ gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
might_sleep_if(gfp_mask & __GFP_WAIT);
repeat_alloc:
_
