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    SubjectRe: [PATCH 01/42] percpu counter: clean up percpu_counter_sum_and_set()
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    On Thu, 2008-10-09 at 00:05 -0400, Theodore Ts'o wrote:
    > From: Mingming Cao <cmm@us.ibm.com>
    >
    > percpu_counter_sum_and_set() and percpu_counter_sum() is the same except
    > the former updates the global counter after accounting. Since we are
    > taking the fbc->lock to calculate the precise value of the counter in
    > percpu_counter_sum() anyway, it should simply set fbc->count too, as the
    > percpu_counter_sum_and_set() does.
    >
    > This patch merge these two interfaces into one.

    I totally missed the patch introducing this _and_set() horror, but this
    does look like a good cleanup.

    Thanks Mingming!

    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

    > Signed-off-by: Mingming Cao <cmm@us.ibm.com>
    > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Cc: <linux-ext4@vger.kernel.org>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    > ---
    > fs/ext4/balloc.c | 2 +-
    > include/linux/percpu_counter.h | 12 +++---------
    > lib/percpu_counter.c | 8 +++-----
    > 3 files changed, 7 insertions(+), 15 deletions(-)
    >
    > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
    > index e9fa960..00a94d5 100644
    > --- a/fs/ext4/balloc.c
    > +++ b/fs/ext4/balloc.c
    > @@ -1624,7 +1624,7 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
    > #ifdef CONFIG_SMP
    > if (free_blocks - root_blocks < FBC_BATCH)
    > free_blocks =
    > - percpu_counter_sum_and_set(&sbi->s_freeblocks_counter);
    > + percpu_counter_sum(&sbi->s_freeblocks_counter);
    > #endif
    > if (free_blocks <= root_blocks)
    > /* we don't have free space */
    > diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
    > index 2083888..9007ccd 100644
    > --- a/include/linux/percpu_counter.h
    > +++ b/include/linux/percpu_counter.h
    > @@ -35,7 +35,7 @@ int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
    > void percpu_counter_destroy(struct percpu_counter *fbc);
    > 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 set);
    > +s64 __percpu_counter_sum(struct percpu_counter *fbc);
    >
    > static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
    > {
    > @@ -44,19 +44,13 @@ static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
    >
    > static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
    > {
    > - s64 ret = __percpu_counter_sum(fbc, 0);
    > + s64 ret = __percpu_counter_sum(fbc);
    > return ret < 0 ? 0 : ret;
    > }
    >
    > -static inline s64 percpu_counter_sum_and_set(struct percpu_counter *fbc)
    > -{
    > - return __percpu_counter_sum(fbc, 1);
    > -}
    > -
    > -
    > static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
    > {
    > - return __percpu_counter_sum(fbc, 0);
    > + return __percpu_counter_sum(fbc);
    > }
    >
    > static inline s64 percpu_counter_read(struct percpu_counter *fbc)
    > diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
    > index 4a8ba4b..a866389 100644
    > --- a/lib/percpu_counter.c
    > +++ b/lib/percpu_counter.c
    > @@ -52,7 +52,7 @@ EXPORT_SYMBOL(__percpu_counter_add);
    > * Add up all the per-cpu counts, return the result. This is a more accurate
    > * but much slower version of percpu_counter_read_positive()
    > */
    > -s64 __percpu_counter_sum(struct percpu_counter *fbc, int set)
    > +s64 __percpu_counter_sum(struct percpu_counter *fbc)
    > {
    > s64 ret;
    > int cpu;
    > @@ -62,11 +62,9 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc, int set)
    > for_each_online_cpu(cpu) {
    > s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
    > ret += *pcount;
    > - if (set)
    > - *pcount = 0;
    > + *pcount = 0;
    > }
    > - if (set)
    > - fbc->count = ret;
    > + fbc->count = ret;
    >
    > spin_unlock(&fbc->lock);
    > return ret;



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