On 08/12/2011 10:56 AM, Eric Dumazet wrote:
Le vendredi 05 août 2011 à 04:35 +0400, Glauber Costa a écrit :This patch lays the foundation for us to limit the dcache size. Each super block can have only a maximum amount of dentries under its sub-tree. Allocation fails if we we're over limit and the cache can't be pruned to free up space for the newcomers. Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx> CC: Dave Chinner<david@xxxxxxxxxxxxx> --- fs/dcache.c | 25 +++++++++++++++++++++++++ fs/super.c | 1 + include/linux/fs.h | 1 + 3 files changed, 27 insertions(+), 0 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index ac19d24..52a0faf 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1180,6 +1180,28 @@ void shrink_dcache_parent(struct dentry * parent) } EXPORT_SYMBOL(shrink_dcache_parent); +static int dcache_mem_check(struct super_block *sb) +{ + int i; + int nr_dentry; + struct shrink_control sc = { + .gfp_mask = GFP_KERNEL, + }; + + do { + nr_dentry = 0; + for_each_possible_cpu(i) + nr_dentry += per_cpu(*sb->s_nr_dentry, i);You seriously want to call this for every __d_alloc() invocation, even if s_nr_dentry_max is the default value (INT_MAX) ?
Well, I guess that special-casing INT_MAX is a good thing. I can include it in the next submission, I like it. Thanks.
On a 4096 cpu machine, it will be _very_ slow. A percpu_counter would be the thing to consider, since you can avoid the for_each_possible_cpu(i) loop if percpu_counter_read() is smaller than sb->s_nr_dentry_max. Check how its done in include/net/tcp.h, tcp_too_many_orphans()
Yeah, I guess I could do that. In fact, my first series used percpu_counters, and then I switched. But looking back, percpu_counters are indeed more suitable. The goal back then was trying to avoid percpu_counter_add, but as it is right now, we trade it for an even worse thing.
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