Messages in this thread Patch in this message | | | Date | Fri, 01 Aug 2008 09:35:26 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH] cpuset: make ntasks to be a monotonic increasing value |
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Paul Jackson wrote: > Bottom line - my priorities for non-critical code paths, most important first: > 1) It must work. > 2) Keep it easy for humans to understand. > 3) Reduce kernel text size. > 4) Reduce CPU cycles. >
I agree, Thank you!
How about this one?
The loop after this patch applied is:
ntasks_now = cgroup_task_count(cs->css.cgroup); while (1) { ntasks = ntasks_now; /* guess */ ntasks += fudge; mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL); if (!mmarray) goto done; read_lock(&tasklist_lock); /* block fork */ ntasks_now = cgroup_task_count(cs->css.cgroup); if (ntasks_now <= ntasks) break; /* got enough */ read_unlock(&tasklist_lock); /* try again */ kfree(mmarray); }
I think the readability of this code is as good as original's. And it's better in semantic meaning.
The old non monotonic increasing value is caused by the redundant cgroup_task_count(). Removing it is good for keeping ntasks increasing(not need additional arithmetic compare or max statement).
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> --- diff --git a/kernel/cpuset.c b/kernel/cpuset.c index d5ab79c..56a057f 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -930,7 +930,7 @@ static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem) { struct task_struct *p; struct mm_struct **mmarray; - int i, n, ntasks; + int i, n, ntasks, ntasks_now; int migrate; int fudge; struct cgroup_iter it; @@ -949,14 +949,16 @@ static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem) * few more lines of code, we can retry until we get a big * enough mmarray[] w/o using GFP_ATOMIC. */ + ntasks_now = cgroup_task_count(cs->css.cgroup); while (1) { - ntasks = cgroup_task_count(cs->css.cgroup); /* guess */ + ntasks = ntasks_now; /* guess */ ntasks += fudge; mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL); if (!mmarray) goto done; read_lock(&tasklist_lock); /* block fork */ - if (cgroup_task_count(cs->css.cgroup) <= ntasks) + ntasks_now = cgroup_task_count(cs->css.cgroup); + if (ntasks_now <= ntasks) break; /* got enough */ read_unlock(&tasklist_lock); /* try again */ kfree(mmarray);
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