From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Scott Cheloha <cheloha@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org,
"Rafael J. Wysocki" <rafael@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
nathanl@linux.ibm.com, ricklind@linux.vnet.ibm.com,
Scott Cheloha <cheloha@linux.ibm.com>,
Donald Dutile <ddutile@redhat.com>
Subject: Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup
Date: Thu, 16 Jan 2020 17:17:54 +0100 [thread overview]
Message-ID: <fe92b4f0-0cd7-c705-1ed9-239175689051@redhat.com> (raw)
In-Reply-To: <765a07fe-47e9-fe3d-716a-44d9ee4a5e99@redhat.com>
On 16.01.20 16:28, David Hildenbrand wrote:
> On 16.01.20 16:22, Michal Hocko wrote:
>> On Wed 15-01-20 20:09:48, David Hildenbrand wrote:
>>> On 09.01.20 22:25, Scott Cheloha wrote:
>>>> Searching for a particular memory block by id is an O(n) operation
>>>> because each memory block's underlying device is kept in an unsorted
>>>> linked list on the subsystem bus.
>>>>
>>>> We can cut the lookup cost to O(log n) if we cache the memory blocks in
>>>> a radix tree. With a radix tree cache in place both memory subsystem
>>>> initialization and memory hotplug run palpably faster on systems with a
>>>> large number of memory blocks.
>>>>
>>>> Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>>> Acked-by: Nathan Lynch <nathanl@linux.ibm.com>
>>>> Acked-by: Michal Hocko <mhocko@suse.com>
>>>
>>> Soooo,
>>>
>>> I just learned that radix trees are nowadays only a wrapper for xarray
>>> (for quite a while already!), and that the xarray interface shall be
>>> used in new code.
>>
>> Good point. I somehow didn't realize this would add more work for a
>> later code refactoring. The mapping should be pretty straightforward.
>
> Yes it is. @Scott, care to send a fixup that does the mapping?
Never having used an xarray, I gave it a quick shot. The following
should do the trick:
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index c6d288fad493..c75dec35de43 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -19,7 +19,7 @@
#include <linux/memory.h>
#include <linux/memory_hotplug.h>
#include <linux/mm.h>
-#include <linux/radix-tree.h>
+#include <linux/xarray.h>
#include <linux/stat.h>
#include <linux/slab.h>
@@ -58,11 +58,11 @@ static struct bus_type memory_subsys = {
};
/*
- * Memory blocks are cached in a local radix tree to avoid
+ * Memory blocks are cached in a local xarray to avoid
* a costly linear search for the corresponding device on
* the subsystem bus.
*/
-static RADIX_TREE(memory_blocks, GFP_KERNEL);
+static DEFINE_XARRAY(memory_blocks);
static BLOCKING_NOTIFIER_HEAD(memory_chain);
@@ -566,7 +566,7 @@ static struct memory_block *find_memory_block_by_id(unsigned long block_id)
{
struct memory_block *mem;
- mem = radix_tree_lookup(&memory_blocks, block_id);
+ mem = xa_load(&memory_blocks, block_id);
if (mem)
get_device(&mem->dev);
return mem;
@@ -621,7 +621,8 @@ int register_memory(struct memory_block *memory)
put_device(&memory->dev);
return ret;
}
- ret = radix_tree_insert(&memory_blocks, memory->dev.id, memory);
+ ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
+ GFP_KERNEL));
if (ret) {
put_device(&memory->dev);
device_unregister(&memory->dev);
@@ -683,7 +684,7 @@ static void unregister_memory(struct memory_block *memory)
if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
return;
- WARN_ON(radix_tree_delete(&memory_blocks, memory->dev.id) == NULL);
+ WARN_ON(xa_erase(&memory_blocks, memory->dev.id) == NULL);
/* drop the ref. we got via find_memory_block() */
put_device(&memory->dev);
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-01-16 16:18 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20191217193238-1-cheloha@linux.vnet.ibm.com>
2020-01-09 21:19 ` [PATCH] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup Scott Cheloha
2020-01-09 21:30 ` Michal Hocko
2020-01-09 21:25 ` [PATCH v4] " Scott Cheloha
2020-01-09 22:00 ` Andrew Morton
2020-01-09 22:17 ` David Hildenbrand
2020-01-09 22:27 ` Andrew Morton
2020-01-09 22:35 ` David Hildenbrand
2020-01-10 9:32 ` David Hildenbrand
2020-01-10 11:31 ` Michal Hocko
2020-01-15 19:09 ` David Hildenbrand
2020-01-16 15:22 ` Michal Hocko
2020-01-16 15:28 ` David Hildenbrand
2020-01-16 16:17 ` David Hildenbrand [this message]
2020-01-17 9:35 ` Michal Hocko
2020-01-20 9:15 ` David Hildenbrand
2020-01-21 12:30 ` Michal Hocko
2020-01-16 17:17 ` Don Dutile
2020-01-21 23:10 ` [PATCH v5] drivers/base/memory.c: cache memory blocks in xarray " Scott Cheloha
2020-01-22 10:43 ` David Hildenbrand
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