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authorRoman Gushchin <guro@fb.com>2019-05-07 20:01:47 +0300
committerDennis Zhou <dennis@kernel.org>2019-05-09 20:49:47 +0300
commit09ed79d6d75f06cc963a78f25463251b0a758dc7 (patch)
tree379de15651feaf475945ab05fca4d6acd69ba32e /include/linux/percpu-refcount.h
parente93c9c99a629c61837d5a7fc2120cd2b6c70dbdd (diff)
downloadlinux-09ed79d6d75f06cc963a78f25463251b0a758dc7.tar.xz
percpu_ref: introduce PERCPU_REF_ALLOW_REINIT flag
In most cases percpu reference counters are not switched to the percpu mode after they reach the atomic mode. Some obvious exceptions are reference counters which are initialized into the atomic mode (using PERCPU_REF_INIT_ATOMIC and PERCPU_REF_INIT_DEAD flags), and there are few other exceptions. But in most cases there is no way back, and once the reference counter is switched to the atomic mode, there is no reason to wait for percpu_ref_exit() to release the percpu memory. Of course, the size of a single counter is not so big, but because it can pin the whole percpu block in memory, the memory footprint can be noticeable (e.g. on my 32 CPUs machine a percpu block is 8Mb large). To make releasing of the percpu memory as early as possible, let's introduce the PERCPU_REF_ALLOW_REINIT flag with the following semantics: it has to be set in order to switch a percpu reference counter to the percpu mode after the initialization. PERCPU_REF_INIT_ATOMIC and PERCPU_REF_INIT_DEAD flags will implicitly assume PERCPU_REF_ALLOW_REINIT. This patch doesn't introduce any functional change to avoid any regressions. It will be done later in the patchset after adjusting all call sites, which are reviving percpu counters. Signed-off-by: Roman Gushchin <guro@fb.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Dennis Zhou <dennis@kernel.org>
Diffstat (limited to 'include/linux/percpu-refcount.h')
-rw-r--r--include/linux/percpu-refcount.h9
1 files changed, 8 insertions, 1 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index b297cd1cd4f1..0f0240af8520 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -75,14 +75,21 @@ enum {
* operation using percpu_ref_switch_to_percpu(). If initialized
* with this flag, the ref will stay in atomic mode until
* percpu_ref_switch_to_percpu() is invoked on it.
+ * Implies ALLOW_REINIT.
*/
PERCPU_REF_INIT_ATOMIC = 1 << 0,
/*
* Start dead w/ ref == 0 in atomic mode. Must be revived with
- * percpu_ref_reinit() before used. Implies INIT_ATOMIC.
+ * percpu_ref_reinit() before used. Implies INIT_ATOMIC and
+ * ALLOW_REINIT.
*/
PERCPU_REF_INIT_DEAD = 1 << 1,
+
+ /*
+ * Allow switching from atomic mode to percpu mode.
+ */
+ PERCPU_REF_ALLOW_REINIT = 1 << 2,
};
struct percpu_ref {