Re: [PATCH 03/16] [RFC] xfs: use generic per-cpu counter infrastructure

Christoph Hellwig
2010-11-08T12:11:57Z

On Mon, Nov 08, 2010 at 07:55:06PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> XFS has a per-cpu counter implementation for in-core superblock
> counters that pre-dated the generic implementation. It is complex
> and baroque as it is tailored directly to the needs of ENOSPC
> detection. Implement the complex accurate-compare-and-add
> calculation in the generic per-cpu counter code and convert the
> XFS counters to use the much simpler generic counter code.
>
> Passes xfsqa on SMP system.

Some mostly cosmetic comments below. I haven't looked at the more
hairy bits like the changes to the generic percpu code and the
reservation handling yet.

> 1. kill the no-per-cpu-counter mode?

already done.

> 3. do we need to factor xfs_mod_sb_incore()?

Doesn't exist anymore.

> - xfs_icsb_sync_counters(mp, XFS_ICSB_LAZY_COUNT);
> + xfs_icsb_sync_counters(mp);
> spin_lock(&mp->m_sb_lock);

Can be moved inside the lock and use the unlocked version, too.

> +static inline int
> +xfs_icsb_add(
> + struct xfs_mount *mp,
> + int counter,
> + int64_t delta,
> + int64_t threshold)
> +{
> + int ret;
> +
> + ret = percpu_counter_add_unless_lt(&mp->m_icsb[counter], delta,
> + threshold);
> + if (ret < 0)
> + return -ENOSPC;
> + return 0;
> +}
> +
> +static inline void
> +xfs_icsb_set(
> + struct xfs_mount *mp,
> + int counter,
> + int64_t value)
> +{
> + percpu_counter_set(&mp->m_icsb[counter], value);
> +}
> +
> +static inline int64_t
> +xfs_icsb_sum(
> + struct xfs_mount *mp,
> + int counter)
> +{
> + return percpu_counter_sum_positive(&mp->m_icsb[counter]);
> +}
> +
> +static inline int64_t
> +xfs_icsb_read(
> + struct xfs_mount *mp,
> + int counter)
> +{
> + return percpu_counter_read_positive(&mp->m_icsb[counter]);
> +}

I would just opencode all these helpers in their callers. There's
generally just one caller of each, which iterates over the three
counters anyway.

> +int
> +xfs_icsb_modify_counters(
> + xfs_mount_t *mp,
> + xfs_sb_field_t field,
> + int64_t delta,
> + int rsvd)

I can't see the point of keeping this multiplexer. The inode counts
are handled entirely different from the block count, so they should
have separate functions.

> +{
> + int64_t lcounter;
> + int64_t res_used;
> + int ret = 0;
> +
> +
> + switch (field) {
> + case XFS_SBS_ICOUNT:
> + ret = xfs_icsb_add(mp, XFS_ICSB_ICOUNT, delta, 0);
> + if (ret < 0) {
> + ASSERT(0);
> + return XFS_ERROR(EINVAL);
> + }
> + return 0;
> +
> + case XFS_SBS_IFREE:
> + ret = xfs_icsb_add(mp, XFS_ICSB_IFREE, delta, 0);
> + if (ret < 0) {
> + ASSERT(0);
> + return XFS_ERROR(EINVAL);
> + }
> + return 0;

If you're keeping a common helper for both inode counts this can be
simplified by sharing the code and just passing on the field instead
of having two cases.

> + struct percpu_counter m_icsb[XFS_ICSB_MAX];

I wonder if there's all that much of a point in keeping the array.
We basically only use the fact it's an array for the init/destroy
code. Maybe it would be a tad cleaner to just have three separate
percpu counters.

> +static inline void
> +xfs_icsb_sync_counters(
> + struct xfs_mount *mp)
> +{
> + spin_lock(&mp->m_sb_lock);
> + xfs_icsb_sync_counters_locked(mp);
> + spin_unlock(&mp->m_sb_lock);
> +}

There's only one callers of this left after my comment above is
addressed. I'd just make xfs_icsb_sync_counters the locked version,
throw in an assert_spin_locked and have the one remaining caller
take the lock opencoded as well.

> --- a/include/linux/percpu_counter.h
> +++ b/include/linux/percpu_counter.h
> @@ -41,6 +41,8 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
> void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
> s64 __percpu_counter_sum(struct percpu_counter *fbc);
> int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs);
> +int percpu_counter_add_unless_lt(struct percpu_counter *fbc, s64 amount,
> + s64 threshold);
>
> static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
> {
> @@ -153,6 +155,20 @@ static inline int percpu_counter_initialized(struct percpu_counter *fbc)
> return 1;
> }
>
> +static inline int percpu_counter_test_and_add_delta(struct percpu_counter *fbc, s64 delta)

This doesn't match the function provided for CONFIG_SMP.

> +/**
> + *

spurious line.

> +int percpu_counter_add_unless_lt(struct percpu_counter *fbc, s64 amount, s64
> +threshold)

too long line