From: Gregory Price <gourry.memverge@gmail.com>
To: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
corbet@lwn.net, akpm@linux-foundation.org,
gregory.price@memverge.com, honggyu.kim@sk.com, rakie.kim@sk.com,
hyeongtak.ji@sk.com, mhocko@kernel.org, ying.huang@intel.com,
vtavarespetr@micron.com, jgroves@micron.com,
ravis.opensrc@micron.com, sthanneeru@micron.com,
emirakhur@micron.com, Hasan.Maruf@amd.com,
seungjun.ha@samsung.com, hannes@cmpxchg.org,
dan.j.williams@intel.com
Subject: [PATCH 2/3] mm/mempolicy: refactor a read-once mechanism into a function for re-use
Date: Fri, 12 Jan 2024 16:08:33 -0500 [thread overview]
Message-ID: <20240112210834.8035-3-gregory.price@memverge.com> (raw)
In-Reply-To: <20240112210834.8035-1-gregory.price@memverge.com>
move the use of barrier() to force policy->nodemask onto the stack into
a function `read_once_policy_nodemask` so that it may be re-used.
Suggested-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
---
mm/mempolicy.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5da4fd79fd18..0abd3a3394ef 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1907,6 +1907,20 @@ unsigned int mempolicy_slab_node(void)
}
}
+static unsigned int read_once_policy_nodemask(struct mempolicy *pol,
+ nodemask_t *mask)
+{
+ /*
+ * barrier stabilizes the nodemask locally so that it can be iterated
+ * over safely without concern for changes. Allocators validate node
+ * selection does not violate mems_allowed, so this is safe.
+ */
+ barrier();
+ __builtin_memcpy(mask, &pol->nodes, sizeof(nodemask_t));
+ barrier();
+ return nodes_weight(*mask);
+}
+
/*
* Do static interleaving for interleave index @ilx. Returns the ilx'th
* node in pol->nodes (starting from ilx=0), wrapping around if ilx
@@ -1914,20 +1928,12 @@ unsigned int mempolicy_slab_node(void)
*/
static unsigned int interleave_nid(struct mempolicy *pol, pgoff_t ilx)
{
- nodemask_t nodemask = pol->nodes;
+ nodemask_t nodemask;
unsigned int target, nnodes;
int i;
int nid;
- /*
- * The barrier will stabilize the nodemask in a register or on
- * the stack so that it will stop changing under the code.
- *
- * Between first_node() and next_node(), pol->nodes could be changed
- * by other threads. So we put pol->nodes in a local stack.
- */
- barrier();
- nnodes = nodes_weight(nodemask);
+ nnodes = read_once_policy_nodemask(pol, &nodemask);
if (!nnodes)
return numa_node_id();
target = ilx % nnodes;
--
2.39.1
next prev parent reply other threads:[~2024-01-12 21:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-12 21:08 [PATCH 0/3] mm/mempolicy: weighted interleave mempolicy with sysfs extension Gregory Price
2024-01-12 21:08 ` Gregory Price [this message]
2024-01-15 4:13 ` [PATCH 2/3] mm/mempolicy: refactor a read-once mechanism into a function for re-use Huang, Ying
2024-01-17 5:26 ` Gregory Price
[not found] ` <20240112210834.8035-2-gregory.price@memverge.com>
2024-01-15 3:18 ` [PATCH 1/3] mm/mempolicy: implement the sysfs-based weighted_interleave interface Huang, Ying
2024-01-17 5:24 ` Gregory Price
2024-01-17 6:58 ` Huang, Ying
2024-01-17 17:46 ` Gregory Price
2024-01-18 4:37 ` Huang, Ying
[not found] ` <20240112210834.8035-4-gregory.price@memverge.com>
2024-01-15 5:47 ` [PATCH 3/3] mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving Huang, Ying
2024-01-17 5:34 ` Gregory Price
2024-01-18 1:28 ` Huang, Ying
2024-01-18 3:05 ` Huang, Ying
2024-01-18 4:06 ` Gregory Price
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