On Fri, 22 Dec 2006 23:25:16 +0300
Alex Tomas <alex@xxxxxxxxxxxxx> 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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