The patch titled
Subject: mm: vmalloc: add va_alloc() helper
has been added to the -mm mm-unstable branch. Its filename is
mm-vmalloc-add-va_alloc-helper.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmalloc-add-va_alloc-helper.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
Subject: mm: vmalloc: add va_alloc() helper
Date: Tue, 2 Jan 2024 19:46:23 +0100
Patch series "Mitigate a vmap lock contention", v3.
1. Motivation
- Offload global vmap locks making it scaled to number of CPUS;
- If possible and there is an agreement, we can remove the "Per cpu kva
allocator" to make the vmap code to be more simple;
- There were complaints from XFS folk that a vmalloc might be contented
on their workloads.
2. Design(high level overview)
We introduce an effective vmap node logic. A node behaves as independent
entity to serve an allocation request directly(if possible) from its pool.
That way it bypasses a global vmap space that is protected by its own
lock.
An access to pools are serialized by CPUs. Number of nodes are equal to
number of CPUs in a system. Please note the high threshold is bound to
128 nodes.
Pools are size segregated and populated based on system demand. The
maximum alloc request that can be stored into a segregated storage is 256
pages. The lazily drain path decays a pool by 25% as a first step and as
second populates it by fresh freed VAs for reuse instead of returning them
into a global space.
When a VA is obtained(alloc path), it is stored in separate nodes. A
va->va_start address is converted into a correct node where it should be
placed and resided. Doing so we balance VAs across the nodes as a result
an access becomes scalable. The addr_to_node() function does a proper
address conversion to a correct node.
A vmap space is divided on segments with fixed size, it is 16 pages. That
way any address can be associated with a segment number. Number of
segments are equal to num_possible_cpus() but not grater then 128. The
numeration starts from 0. See below how it is converted:
static inline unsigned int
addr_to_node_id(unsigned long addr)
{
return (addr / zone_size) % nr_nodes;
}
On a free path, a VA can be easily found by converting its "va_start"
address to a certain node it resides. It is moved from "busy" data to
"lazy" data structure. Later on, as noted earlier, the lazy kworker
decays each node pool and populates it by fresh incoming VAs. Please
note, a VA is returned to a node that did an alloc request.
3. Test on AMD Ryzen Threadripper 3970X 32-Core Processor
sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64
<default perf>
94.41% 0.89% [kernel] [k] _raw_spin_lock
93.35% 93.07% [kernel] [k] native_queued_spin_lock_slowpath
76.13% 0.28% [kernel] [k] __vmalloc_node_range
72.96% 0.81% [kernel] [k] alloc_vmap_area
56.94% 0.00% [kernel] [k] __get_vm_area_node
41.95% 0.00% [kernel] [k] vmalloc
37.15% 0.01% [test_vmalloc] [k] full_fit_alloc_test
35.17% 0.00% [kernel] [k] ret_from_fork_asm
35.17% 0.00% [kernel] [k] ret_from_fork
35.17% 0.00% [kernel] [k] kthread
35.08% 0.00% [test_vmalloc] [k] test_func
34.45% 0.00% [test_vmalloc] [k] fix_size_alloc_test
28.09% 0.01% [test_vmalloc] [k] long_busy_list_alloc_test
23.53% 0.25% [kernel] [k] vfree.part.0
21.72% 0.00% [kernel] [k] remove_vm_area
20.08% 0.21% [kernel] [k] find_unlink_vmap_area
2.34% 0.61% [kernel] [k] free_vmap_area_noflush
<default perf>
vs
<patch-series perf>
82.32% 0.22% [test_vmalloc] [k] long_busy_list_alloc_test
63.36% 0.02% [kernel] [k] vmalloc
63.34% 2.64% [kernel] [k] __vmalloc_node_range
30.42% 4.46% [kernel] [k] vfree.part.0
28.98% 2.51% [kernel] [k] __alloc_pages_bulk
27.28% 0.19% [kernel] [k] __get_vm_area_node
26.13% 1.50% [kernel] [k] alloc_vmap_area
21.72% 21.67% [kernel] [k] clear_page_rep
19.51% 2.43% [kernel] [k] _raw_spin_lock
16.61% 16.51% [kernel] [k] native_queued_spin_lock_slowpath
13.40% 2.07% [kernel] [k] free_unref_page
10.62% 0.01% [kernel] [k] remove_vm_area
9.02% 8.73% [kernel] [k] insert_vmap_area
8.94% 0.00% [kernel] [k] ret_from_fork_asm
8.94% 0.00% [kernel] [k] ret_from_fork
8.94% 0.00% [kernel] [k] kthread
8.29% 0.00% [test_vmalloc] [k] test_func
7.81% 0.05% [test_vmalloc] [k] full_fit_alloc_test
5.30% 4.73% [kernel] [k] purge_vmap_node
4.47% 2.65% [kernel] [k] free_vmap_area_noflush
<patch-series perf>
confirms that a native_queued_spin_lock_slowpath goes down to
16.51% percent from 93.07%.
The throughput is ~12x higher:
urezki@pc638:~$ time sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64
Run the test with following parameters: run_test_mask=7 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.
real 10m51.271s
user 0m0.013s
sys 0m0.187s
urezki@pc638:~$
urezki@pc638:~$ time sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64
Run the test with following parameters: run_test_mask=7 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.
real 0m51.301s
user 0m0.015s
sys 0m0.040s
urezki@pc638:~$
This patch (of 11):
Currently __alloc_vmap_area() function contains an open codded logic that
finds and adjusts a VA based on allocation request.
Introduce a va_alloc() helper that adjusts found VA only. There is no a
functional change as a result of this patch.
Link: https://lkml.kernel.org/r/20240102184633.748113-1-urezki@xxxxxxxxx
Link: https://lkml.kernel.org/r/20240102184633.748113-2-urezki@xxxxxxxxx
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@xxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 41 ++++++++++++++++++++++++++++-------------
1 file changed, 28 insertions(+), 13 deletions(-)
--- a/mm/vmalloc.c~mm-vmalloc-add-va_alloc-helper
+++ a/mm/vmalloc.c
@@ -1481,6 +1481,32 @@ adjust_va_to_fit_type(struct rb_root *ro
return 0;
}
+static unsigned long
+va_alloc(struct vmap_area *va,
+ struct rb_root *root, struct list_head *head,
+ unsigned long size, unsigned long align,
+ unsigned long vstart, unsigned long vend)
+{
+ unsigned long nva_start_addr;
+ int ret;
+
+ if (va->va_start > vstart)
+ nva_start_addr = ALIGN(va->va_start, align);
+ else
+ nva_start_addr = ALIGN(vstart, align);
+
+ /* Check the "vend" restriction. */
+ if (nva_start_addr + size > vend)
+ return vend;
+
+ /* Update the free vmap_area. */
+ ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
+ if (WARN_ON_ONCE(ret))
+ return vend;
+
+ return nva_start_addr;
+}
+
/*
* Returns a start address of the newly allocated area, if success.
* Otherwise a vend is returned that indicates failure.
@@ -1493,7 +1519,6 @@ __alloc_vmap_area(struct rb_root *root,
bool adjust_search_size = true;
unsigned long nva_start_addr;
struct vmap_area *va;
- int ret;
/*
* Do not adjust when:
@@ -1511,18 +1536,8 @@ __alloc_vmap_area(struct rb_root *root,
if (unlikely(!va))
return vend;
- if (va->va_start > vstart)
- nva_start_addr = ALIGN(va->va_start, align);
- else
- nva_start_addr = ALIGN(vstart, align);
-
- /* Check the "vend" restriction. */
- if (nva_start_addr + size > vend)
- return vend;
-
- /* Update the free vmap_area. */
- ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
- if (WARN_ON_ONCE(ret))
+ nva_start_addr = va_alloc(va, root, head, size, align, vstart, vend);
+ if (nva_start_addr == vend)
return vend;
#if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
_
Patches currently in -mm which might be from urezki@xxxxxxxxx are
mm-vmalloc-add-va_alloc-helper.patch
mm-vmalloc-rename-adjust_va_to_fit_type-function.patch
mm-vmalloc-move-vmap_init_free_space-down-in-vmallocc.patch
mm-vmalloc-remove-global-vmap_area_root-rb-tree.patch
mm-vmalloc-remove-global-purge_vmap_area_root-rb-tree.patch
mm-vmalloc-offload-free_vmap_area_lock-lock.patch
mm-vmalloc-support-multiple-nodes-in-vread_iter.patch
mm-vmalloc-support-multiple-nodes-in-vmallocinfo.patch
mm-vmalloc-set-nr_nodes-based-on-cpus-in-a-system.patch
mm-vmalloc-add-a-shrinker-to-drain-vmap-pools.patch
