On Fri, Mar 03 2017, Shaohua Li wrote: > On Fri, Mar 03, 2017 at 02:03:31PM +1100, Neil Brown wrote: >> On Fri, Feb 17 2017, Shaohua Li wrote: >> >> > Bump the flush stripe batch size to 2048. For my 12 disks raid >> > array, the stripes takes: >> > 12 * 4k * 2048 = 96MB >> > >> > This is still quite small. A hardware raid card generally has 1GB size, >> > which we suggest the raid5-cache has similar cache size. >> > >> > The advantage of a big batch size is we can dispatch a lot of IO in the >> > same time, then we can do some scheduling to make better IO pattern. >> > >> > Last patch prioritizes stripes, so we don't worry about a big flush >> > stripe batch will starve normal stripes. >> > >> > Signed-off-by: Shaohua Li <shli@xxxxxx> >> > --- >> > drivers/md/raid5-cache.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c >> > index 3f307be..b25512c 100644 >> > --- a/drivers/md/raid5-cache.c >> > +++ b/drivers/md/raid5-cache.c >> > @@ -43,7 +43,7 @@ >> > /* wake up reclaim thread periodically */ >> > #define R5C_RECLAIM_WAKEUP_INTERVAL (30 * HZ) >> > /* start flush with these full stripes */ >> > -#define R5C_FULL_STRIPE_FLUSH_BATCH 256 >> > +#define R5C_FULL_STRIPE_FLUSH_BATCH 2048 >> >> Fixed numbers are warning signs... I wonder if there is something better >> we could do? "conf->max_nr_stripes / 4" maybe? We use that sort of >> number elsewhere. >> Would that make sense? > > The code where we check the batch size (in r5c_do_reclaim) already a check: > total_cached > conf->min_nr_stripes * 1 / 2 > so I think that's ok, no? I'm not sure what you are saying. I'm suggesting that we get rid of R5C_FULL_STRIPE_FLUSH_BATCH and use a number like "conf->max_nr_stripes / 4" Are you agreeing, or are you saying that you don't think we need to get rid of R5C_FULL_STRIPE_FLUSH_BATCH?? Thanks, NeilBrown
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