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Message-ID: <ZwiRdemGMY6Z6pSN@xsang-OptiPlex-9020>
Date: Fri, 11 Oct 2024 10:46:13 +0800
From: Oliver Sang <oliver.sang@...el.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
CC: <oe-lkp@...ts.linux.dev>, <lkp@...el.com>, <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, Mark Brown <broonie@...nel.org>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
<vbabka@...e.cz>, Bert Karwatzki <spasswolf@....de>, Jeff Xu
<jeffxu@...omium.org>, Jiri Olsa <olsajiri@...il.com>, Kees Cook
<kees@...nel.org>, Lorenzo Stoakes <lstoakes@...il.com>, Matthew Wilcox
<willy@...radead.org>, "Paul E. McKenney" <paulmck@...nel.org>, Paul Moore
<paul@...l-moore.com>, Sidhartha Kumar <sidhartha.kumar@...cle.com>, "Suren
Baghdasaryan" <surenb@...gle.com>, <linux-mm@...ck.org>,
<ying.huang@...el.com>, <feng.tang@...el.com>, <fengwei.yin@...el.com>,
<oliver.sang@...el.com>
Subject: Re: [linus:master] [mm] cacded5e42: aim9.brk_test.ops_per_sec
-5.0% regression
hi, Lorenzo,
On Wed, Oct 09, 2024 at 10:24:58PM +0100, Lorenzo Stoakes wrote:
> On Wed, Oct 09, 2024 at 02:44:30PM +0800, Oliver Sang wrote:
> [snip]
> > >
> > > I will look into this now, if I provide patches would you be able to test
> > > them using the same boxes? It'd be much appreciated!
> >
> > sure! that's our pleasure!
> >
>
> Hi Oliver,
>
> Thanks so much for this, could you give the below a try? I've not tried to
> seriously test it locally yet, so it'd be good to set your test machines on
> it.
>
> If this doesn't help it suggests call stack/branching might be a thing here
> in which case I have other approaches I can take before we have to
> duplicate this code.
>
> This patch is against the mm-unstable branch in Andrew's tree [0] but
> hopefully should apply fine to Linus's too.
>
> [0]:https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/
>
> Thanks again!
you are welcome!
I found the patch could be applied directly on cacded5e42, so I did it.
this is our normal practice that we want to avoid impacts from other commits.
but if your patch should reply on some new patches in mm-unstable or mainline,
please let me know. I could reapply and retest.
I mentioned patch base since I found by my applyment upon cacded5e42, your
patch seems not have obvious performance impact, still have similar regression.
for brief, I just list 2 examples here. all tests and full data are attached
as fc21959f74bc11-cacded5e42b960-2e71337ac26478
(1)
model: Sapphire Rapids
nr_node: 2
nr_cpu: 224
memory: 512G
brand: Intel(R) Xeon(R) Platinum 8480CTDX
=========================================================================================
compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase/testtime:
gcc-12/performance/x86_64-rhel-8.3/debian-12-x86_64-20240206.cgz/lkp-spr-2sp4/brk_test/aim9/300s
commit:
fc21959f74bc11 ("mm: abstract vma_expand() to use vma_merge_struct")
cacded5e42b960 ("mm: avoid using vma_merge() for new VMAs")
2e71337ac26478 ("mm: explicitly enable an expand-only merge mode for brk()")
fc21959f74bc1138 cacded5e42b9609b07b22d80c10 2e71337ac2647889d3d9d76a5ce
---------------- --------------------------- ---------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
3540976 -6.4% 3314159 -6.7% 3302864 aim9.brk_test.ops_per_sec
(2) which is using same Ivy Bridge-EP in our original report
(test machine: 48 threads 2 sockets Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz (Ivy Bridge-EP) with 64G memory)
=========================================================================================
compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase/testtime:
gcc-12/performance/x86_64-rhel-8.3/debian-12-x86_64-20240206.cgz/lkp-ivb-2ep2/brk_test/aim9/300s
commit:
fc21959f74bc11 ("mm: abstract vma_expand() to use vma_merge_struct")
cacded5e42b960 ("mm: avoid using vma_merge() for new VMAs")
2e71337ac26478 ("mm: explicitly enable an expand-only merge mode for brk()")
fc21959f74bc1138 cacded5e42b9609b07b22d80c10 2e71337ac2647889d3d9d76a5ce
---------------- --------------------------- ---------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
1322908 -5.0% 1256536 -4.1% 1268145 aim9.brk_test.ops_per_sec
>
> Best, Lorenzo
>
>
> ----8<----
> From 7eb4aa421b357668bc44405c58b0444abf44334a Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date: Wed, 9 Oct 2024 21:57:03 +0100
> Subject: [PATCH] mm: explicitly enable an expand-only merge mode for brk()
>
> Try to do less work on brk() to improve perf.
> ---
> mm/mmap.c | 1 +
> mm/vma.c | 25 ++++++++++++++++---------
> mm/vma.h | 11 +++++++++++
> 3 files changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 02f7b45c3076..c2c68ef45a3b 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1740,6 +1740,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
> if (vma && vma->vm_end == addr) {
> VMG_STATE(vmg, mm, vmi, addr, addr + len, flags, PHYS_PFN(addr));
>
> + vmg.mode = VMA_MERGE_MODE_EXPAND_ONLY;
> vmg.prev = vma;
> vma_iter_next_range(vmi);
>
> diff --git a/mm/vma.c b/mm/vma.c
> index 749c4881fd60..f525a0750c41 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -561,6 +561,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
> unsigned long end = vmg->end;
> pgoff_t pgoff = vmg->pgoff;
> pgoff_t pglen = PHYS_PFN(end - start);
> + bool expand_only = vmg_mode_expand_only(vmg);
> bool can_merge_left, can_merge_right;
>
> mmap_assert_write_locked(vmg->mm);
> @@ -575,7 +576,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
> return NULL;
>
> can_merge_left = can_vma_merge_left(vmg);
> - can_merge_right = can_vma_merge_right(vmg, can_merge_left);
> + can_merge_right = !expand_only && can_vma_merge_right(vmg, can_merge_left);
>
> /* If we can merge with the next VMA, adjust vmg accordingly. */
> if (can_merge_right) {
> @@ -603,13 +604,18 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
> return vmg->vma;
> }
>
> - /* If expansion failed, reset state. Allows us to retry merge later. */
> - vmg->vma = NULL;
> - vmg->start = start;
> - vmg->end = end;
> - vmg->pgoff = pgoff;
> - if (vmg->vma == prev)
> - vma_iter_set(vmg->vmi, start);
> + /*
> + * Unless in expand only case and expansion failed, reset state.
> + * Allows us to retry merge later.
> + */
> + if (!expand_only) {
> + vmg->vma = NULL;
> + vmg->start = start;
> + vmg->end = end;
> + vmg->pgoff = pgoff;
> + if (vmg->vma == prev)
> + vma_iter_set(vmg->vmi, start);
> + }
>
> return NULL;
> }
> @@ -641,7 +647,8 @@ int vma_expand(struct vma_merge_struct *vmg)
> mmap_assert_write_locked(vmg->mm);
>
> vma_start_write(vma);
> - if (next && (vma != next) && (vmg->end == next->vm_end)) {
> + if (!vmg_mode_expand_only(vmg) && next &&
> + (vma != next) && (vmg->end == next->vm_end)) {
> int ret;
>
> remove_next = true;
> diff --git a/mm/vma.h b/mm/vma.h
> index 82354fe5edd0..14224b36a979 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -52,6 +52,11 @@ struct vma_munmap_struct {
> unsigned long data_vm;
> };
>
> +enum vma_merge_mode {
> + VMA_MERGE_MODE_NORMAL,
> + VMA_MERGE_MODE_EXPAND_ONLY,
> +};
> +
> enum vma_merge_state {
> VMA_MERGE_START,
> VMA_MERGE_ERROR_NOMEM,
> @@ -75,9 +80,15 @@ struct vma_merge_struct {
> struct mempolicy *policy;
> struct vm_userfaultfd_ctx uffd_ctx;
> struct anon_vma_name *anon_name;
> + enum vma_merge_mode mode;
> enum vma_merge_state state;
> };
>
> +static inline bool vmg_mode_expand_only(struct vma_merge_struct *vmg)
> +{
> + return vmg->mode == VMA_MERGE_MODE_EXPAND_ONLY;
> +}
> +
> static inline bool vmg_nomem(struct vma_merge_struct *vmg)
> {
> return vmg->state == VMA_MERGE_ERROR_NOMEM;
> --
> 2.46.2
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