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percpu_counter: FBC_BATCH should be a variable

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For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS

Considering more and more distros are using high NR_CPUS values, it makes
sense to use a more sensible value for FBC_BATCH, and get rid of NR_CPUS.

A sensible value is 2*num_online_cpus(), with a minimum value of 32 (This
minimum value helps branch prediction in __percpu_counter_add())

We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

We rename FBC_BATCH to percpu_counter_batch since its not a constant
anymore.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet
2009-01-06 14:41:04 -08:00
committed by Linus Torvalds
parent e3d5a27d58
commit 179f7ebff6
4 changed files with 20 additions and 14 deletions
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6
fs/ext4/ext4.h
View File

@@ -1225,11 +1225,11 @@ do { \
} while (0)
#ifdef CONFIG_SMP
/* Each CPU can accumulate FBC_BATCH blocks in their local
/* Each CPU can accumulate percpu_counter_batch blocks in their local
* counters. So we need to make sure we have free blocks more
* than FBC_BATCH * nr_cpu_ids. Also add a window of 4 times.
* than percpu_counter_batch * nr_cpu_ids. Also add a window of 4 times.
*/
#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))
#define EXT4_FREEBLOCKS_WATERMARK (4 * (percpu_counter_batch * nr_cpu_ids))
#else
#define EXT4_FREEBLOCKS_WATERMARK 0
#endif

2
fs/ext4/inode.c
View File

@@ -2498,7 +2498,7 @@ static int ext4_nonda_switch(struct super_block *sb)
/*
* switch to non delalloc mode if we are running low
* on free block. The free block accounting via percpu
* counters can get slightly wrong with FBC_BATCH getting
* counters can get slightly wrong with percpu_counter_batch getting
* accumulated on each CPU without updating global counters
* Delalloc need an accurate free block accounting. So switch
* to non delalloc when we are near to error range.