Messages in this thread | | | Date | Sat, 23 Dec 2006 14:40:59 -0800 | From | Andrew Morton <> | Subject | Re: [RFC] ext4-block-reservation.patch |
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On Fri, 22 Dec 2006 23:25:16 +0300 Alex Tomas <alex@clusterfs.com> wrote:
Once this code is settled in we should consider removal of the existing reservations code from ext4.
> + > +struct ext4_reservation_slot { > + __u64 rs_reserved; > + spinlock_t rs_lock; > +} ____cacheline_aligned;
Should be ____cacheline_aligned_in_smp.
That's assuming it needs to be cacheline aligned at all. It can consume a lot of space.
<looks>
oh, this should be allocated with alloc_percpu(), in which case the open-coded alignment can perhaps go away.
> + > +int ext4_reserve_local(struct super_block *sb, int blocks) > +{ > + struct ext4_sb_info *sbi = EXT4_SB(sb); > + struct ext4_reservation_slot *rs; > + int rc = -ENOSPC; > + > + preempt_disable(); > + rs = sbi->s_reservation_slots + smp_processor_id();
use get_cpu() here.
> +void ext4_rebalance_reservation(struct ext4_reservation_slot *rs, __u64 free) > +{ > + int i, used_slots = 0; > + __u64 chunk; > + > + /* let's know what slots have been used */ > + for (i = 0; i < NR_CPUS; i++) > + if (rs[i].rs_reserved || i == smp_processor_id()) > + used_slots++; > + > + /* chunk is a number of block every used > + * slot will get. make sure it isn't 0 */ > + chunk = free + used_slots - 1; > + do_div(chunk, used_slots); > + > + for (i = 0; i < NR_CPUS; i++) {
all these NR_CPUS loops need to go away. Use either for_each_possible_cpu() or, preferably, for_each_online_cpu() and a hotplug notifier.
Why is this code using per-cpu data at all, btw? These optimisations tend to be marginal in filesystems. What is the perfomance impact of making this data be single-superblock-wide-instance?
> +int ext4_reserve_init(struct super_block *sb) > +{ > + struct ext4_sb_info *sbi = EXT4_SB(sb); > + struct ext4_reservation_slot *rs; > + int i; > + > + rs = kmalloc(sizeof(struct ext4_reservation_slot) * NR_CPUS, GFP_KERNEL);
alloc_percpu()
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