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Date: Wed, 11 Mar 2009 15:11:17 -0700
From: Dave Hansen <dave@...ux.vnet.ibm.com>
To: Nick Piggin <npiggin@...e.de>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 1/2] fs: mnt_want_write speedup
I'm feeling a bit better about these, although I am still honestly quite
afraid of the barriers. I also didn't like all the #ifdefs much, but
here's some help on that.
How about this on top of what you have as a bit of a cleanup? It gets
rid of all the new #ifdefs in .c files?
Did I miss the use of get_mnt_writers_ptr()? I don't think I actually
saw it used anywhere in this pair of patches, so I've stolen it. I
think gcc should compile all this new stuff down to be basically the
same as you had before. The one thing I'm not horribly sure of is the
"out_free_devname:" label. It shouldn't be reachable in the !SMP case.
I could also consolidate the header #ifdefs into a single one if you
think that looks better.
This is just compile tested, btw.
---
linux-2.6.git-dave/fs/namespace.c | 35 ++++++-------------------------
linux-2.6.git-dave/include/linux/mount.h | 30 ++++++++++++++++++++++++--
2 files changed, 35 insertions(+), 30 deletions(-)
diff -puN include/linux/mount.h~move-ifdefs-take2 include/linux/mount.h
--- linux-2.6.git/include/linux/mount.h~move-ifdefs-take2 2009-03-11 15:01:10.000000000 -0700
+++ linux-2.6.git-dave/include/linux/mount.h 2009-03-11 15:02:01.000000000 -0700
@@ -71,15 +71,41 @@ struct vfsmount {
#endif
};
-static inline int *get_mnt_writers_ptr(struct vfsmount *mnt)
+static inline int *get_mnt_writers_ptr_cpu(struct vfsmount *mnt,
+ int cpu)
{
#ifdef CONFIG_SMP
- return mnt->mnt_writers;
+ return per_cpu_ptr(mnt->mnt_writers, cpu);
#else
return &mnt->mnt_writers;
#endif
}
+static inline int *get_mnt_writers_ptr(struct vfsmount *mnt)
+{
+ return get_mnt_writers_ptr_cpu(mnt, smp_processor_id());
+}
+
+static inline int alloc_mnt_writers(struct vfsmount *mnt)
+{
+#ifdef CONFIG_SMP
+ mnt->mnt_writers = alloc_percpu(int);
+ if (!mnt->mnt_writers)
+ return -ENOMEM;
+#else
+ mnt->mnt_writers = 0;
+#endif
+ return 0;
+}
+
+static inline void free_mnt_writers(struct vfsmount *mnt)
+{
+#ifdef CONFIG_SMP
+ free_percpu(mnt->mnt_writers);
+#endif
+}
+
+
static inline struct vfsmount *mntget(struct vfsmount *mnt)
{
if (mnt)
diff -puN fs/namespace.c~move-ifdefs-take2 fs/namespace.c
--- linux-2.6.git/fs/namespace.c~move-ifdefs-take2 2009-03-11 15:01:10.000000000 -0700
+++ linux-2.6.git-dave/fs/namespace.c 2009-03-11 15:04:05.000000000 -0700
@@ -130,20 +130,14 @@ struct vfsmount *alloc_vfsmnt(const char
INIT_LIST_HEAD(&mnt->mnt_share);
INIT_LIST_HEAD(&mnt->mnt_slave_list);
INIT_LIST_HEAD(&mnt->mnt_slave);
-#ifdef CONFIG_SMP
- mnt->mnt_writers = alloc_percpu(int);
- if (!mnt->mnt_writers)
+ err = alloc_mnt_writers(mnt);
+ if (err)
goto out_free_devname;
-#else
- mnt->mnt_writers = 0;
-#endif
}
return mnt;
-#ifdef CONFIG_SMP
out_free_devname:
kfree(mnt->mnt_devname);
-#endif
out_free_id:
mnt_free_id(mnt);
out_free_cache:
@@ -182,36 +176,23 @@ EXPORT_SYMBOL_GPL(__mnt_is_readonly);
static inline void inc_mnt_writers(struct vfsmount *mnt)
{
-#ifdef CONFIG_SMP
- (*per_cpu_ptr(mnt->mnt_writers, smp_processor_id()))++;
-#else
- mnt->mnt_writers++;
-#endif
+ (*get_mnt_writers_ptr(mnt))++;
}
static inline void dec_mnt_writers(struct vfsmount *mnt)
{
-#ifdef CONFIG_SMP
- (*per_cpu_ptr(mnt->mnt_writers, smp_processor_id()))--;
-#else
- mnt->mnt_writers--;
-#endif
+ (*get_mnt_writers_ptr(mnt))--;
}
static unsigned int count_mnt_writers(struct vfsmount *mnt)
{
-#ifdef CONFIG_SMP
unsigned int count = 0;
int cpu;
- for_each_possible_cpu(cpu) {
- count += *per_cpu_ptr(mnt->mnt_writers, cpu);
- }
+ for_each_possible_cpu(cpu)\
+ count += *get_mnt_writers_ptr_cpu(mnt, cpu);
return count;
-#else
- return mnt->mnt_writers;
-#endif
}
/*
@@ -344,9 +325,7 @@ void free_vfsmnt(struct vfsmount *mnt)
{
kfree(mnt->mnt_devname);
mnt_free_id(mnt);
-#ifdef CONFIG_SMP
- free_percpu(mnt->mnt_writers);
-#endif
+ free_mnt_writers(mnt);
kmem_cache_free(mnt_cache, mnt);
}
_
-- Dave
--
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