Hi,
>>>>> Andrew Morton (AM) writes:
AM> Should be ____cacheline_aligned_in_smp.
AM> That's assuming it needs to be cacheline aligned at all. It can consume a
AM> lot of space.
the idea is to make block reservation cheap because it's called
for every page.
AM> <looks>
AM> oh, this should be allocated with alloc_percpu(), in which case the
AM> open-coded alignment can perhaps go away.
got it.
>> +
>> +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();
AM> use get_cpu() here.
ok.
>> +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++) {
AM> all these NR_CPUS loops need to go away. Use either
AM> for_each_possible_cpu() or, preferably, for_each_online_cpu() and a hotplug
AM> notifier.
hmm, i see.
AM> Why is this code using per-cpu data at all, btw? These optimisations tend
AM> to be marginal in filesystems. What is the perfomance impact of making
AM> this data be single-superblock-wide-instance?
well, even on 2way box a single-lock reservation was in top10.
thanks, Alex
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