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Date:   Mon, 5 Jun 2023 10:44:38 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Peng Zhang <zhangpeng.00@bytedance.com>
Cc:     "Yin, Fengwei" <fengwei.yin@intel.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, "Liu, Yujie" <yujie.liu@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 00/14] Reduce preallocations for maple tree
Message-ID: <20230605144438.rloukl3mccgkfxam@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        "Yin, Fengwei" <fengwei.yin@intel.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, "Liu, Yujie" <yujie.liu@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20230601021605.2823123-1-Liam.Howlett@oracle.com>
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 <4fb5f66d-c8c2-f857-7461-b974154dbc2b@bytedance.com>
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* Peng Zhang <zhangpeng.00@bytedance.com> [230605 10:27]:
>=20
>=20
> =E5=9C=A8 2023/6/5 22:03, Liam R. Howlett =E5=86=99=E9=81=93:
> > * Peng Zhang <zhangpeng.00@bytedance.com> [230605 03:59]:
> > >=20
> > >=20
> > > =E5=9C=A8 2023/6/5 14:18, Yin, Fengwei =E5=86=99=E9=81=93:
> > > >=20
> > > >=20
> > > > On 6/5/2023 12:41 PM, Yin Fengwei wrote:
> > > > > Hi Peng,
> > > > >=20
> > > > > On 6/5/23 11:28, Peng Zhang wrote:
> > > > > >=20
> > > > > >=20
> > > > > > =E5=9C=A8 2023/6/2 16:10, Yin, Fengwei =E5=86=99=E9=81=93:
> > > > > > > Hi Liam,
> > > > > > >=20
> > > > > > > On 6/1/2023 10:15 AM, Liam R. Howlett wrote:
> > > > > > > > Initial work on preallocations showed no regression in perf=
ormance
> > > > > > > > during testing, but recently some users (both on [1] and of=
f [android]
> > > > > > > > list) have reported that preallocating the worst-case numbe=
r of nodes
> > > > > > > > has caused some slow down.=C2=A0 This patch set addresses t=
he number of
> > > > > > > > allocations in a few ways.
> > > > > > > >=20
> > > > > > > > During munmap() most munmap() operations will remove a sing=
le VMA, so
> > > > > > > > leverage the fact that the maple tree can place a single po=
inter at
> > > > > > > > range 0 - 0 without allocating.=C2=A0 This is done by chang=
ing the index in
> > > > > > > > the 'sidetree'.
> > > > > > > >=20
> > > > > > > > Re-introduce the entry argument to mas_preallocate() so tha=
t a more
> > > > > > > > intelligent guess of the node count can be made.
> > > > > > > >=20
> > > > > > > > Patches are in the following order:
> > > > > > > > 0001-0002: Testing framework for benchmarking some operatio=
ns
> > > > > > > > 0003-0004: Reduction of maple node allocation in sidetree
> > > > > > > > 0005:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Small cleanup of do_vmi=
_align_munmap()
> > > > > > > > 0006-0013: mas_preallocate() calculation change
> > > > > > > > 0014:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Change the vma iterator=
 order
> > > > > > > I did run The AIM:page_test on an IceLake 48C/96T + 192G RAM =
platform with
> > > > > > > this patchset.
> > > > > > >=20
> > > > > > > The result has a little bit improvement:
> > > > > > > Base (next-20230602):
> > > > > > >   =C2=A0=C2=A0 503880
> > > > > > > Base with this patchset:
> > > > > > >   =C2=A0=C2=A0 519501
> > > > > > >=20
> > > > > > > But they are far from the none-regression result (commit 7be1=
c1a3c7b1):
> > > > > > >   =C2=A0=C2=A0 718080
> > > > > > >=20
> > > > > > >=20
> > > > > > > Some other information I collected:
> > > > > > > With Base, the mas_alloc_nodes are always hit with request: 7=
.
> > > > > > > With this patchset, the request are 1 or 5.
> > > > > > >=20
> > > > > > > I suppose this is the reason for improvement from 503880 to 5=
19501.
> > > > > > >=20
> > > > > > > With commit 7be1c1a3c7b1, mas_store_gfp() in do_brk_flags nev=
er triggered
> > > > > > > mas_alloc_nodes() call. Thanks.
> > > > > > Hi Fengwei,
> > > > > >=20
> > > > > > I think it may be related to the inaccurate number of nodes all=
ocated
> > > > > > in the pre-allocation. I slightly modified the pre-allocation i=
n this
> > > > > > patchset, but I don't know if it works. It would be great if yo=
u could
> > > > > > help test it, and help pinpoint the cause. Below is the diff, w=
hich can
> > > > > > be applied based on this pachset.
> > > > > I tried the patch, it could eliminate the call of mas_alloc_nodes=
() during
> > > > > the test. But the result of benchmark got a little bit improvemen=
t:
> > > > >     529040
> > > > >=20
> > > > > But it's still much less than none-regression result. I will also=
 double
> > > > > confirm the none-regression result.
> > > > Just noticed that the commit f5715584af95 make validate_mm() two im=
plementation
> > > > based on CONFIG_DEBUG_VM instead of CONFIG_DEBUG_VM_MAPPLE_TREE). I=
 have
> > > > CONFIG_DEBUG_VM but not CONFIG_DEBUG_VM_MAPPLE_TREE defined. So it'=
s not an
> > > > apple to apple.
> >=20
> > You mean "mm: update validate_mm() to use vma iterator" here I guess.  =
I
> > have it as a different commit id in my branch.
> >=20
> > I 'restored' some of the checking because I was able to work around not
> > having the mt_dump() definition with the vma iterator.  I'm now
> > wondering how wide spread CONFIG_DEBUG_VM is used and if I should not
> > have added these extra checks.
> >=20
> > > >=20
> > > >=20
> > > > I disable CONFIG_DEBUG_VM and re-run the test and got:
> > > > Before preallocation change (7be1c1a3c7b1):
> > > >       770100
> > > > After preallocation change (28c5609fb236):
> > > >       680000
> > > > With liam's fix:
> > > >       702100
> > > > plus Peng's fix:
> > > >       725900
> > > Thank you for your test, now it seems that the performance
> > > regression is not so much.
> >=20
> > We are also too strict on the reset during mas_store_prealloc() checkin=
g
> > for a spanning write.  I have a fix for this for v2 of the patch set,
> > although I suspect it will not make a huge difference.
> >=20
> > > >=20
> > > >=20
> > > > Regards
> > > > Yin, Fengwei
> > > >=20
> > > > >=20
> > > > >=20
> > > > > Regards
> > > > > Yin, Fengwei
> > > > >=20
> > > > > >=20
> > > > > > Thanks,
> > > > > > Peng
> > > > > >=20
> > > > > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > > > > > index 5ea211c3f186..e67bf2744384 100644
> > > > > > --- a/lib/maple_tree.c
> > > > > > +++ b/lib/maple_tree.c
> > > > > > @@ -5575,9 +5575,11 @@ int mas_preallocate(struct ma_state *mas=
, void *entry, gfp_t gfp)
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto ask_now=
;
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 }
> > > > > >=20
> > > > > > -=C2=A0=C2=A0=C2=A0 /* New root needs a singe node */
> > > > > > -=C2=A0=C2=A0=C2=A0 if (unlikely(mte_is_root(mas->node)))
> > > > > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto ask_now;
> >=20
> > Why did you drop this?  If we are creating a new root we will only need
> > one node.
> The code below handles the root case perfectly,
> we don't need additional checks.
> 	if (node_size  - 1 <=3D mt_min_slots[wr_mas.type])
> 		request =3D mas_mt_height(mas) * 2 - 1;

Unless we have the minimum for a node, in which case we will fall
through and ask for one node.  This works and is rare enough so I'll
drop it.  Thanks.

> >=20
> > > > > > +=C2=A0=C2=A0=C2=A0 if ((node_size =3D=3D wr_mas.node_end + 1 &=
&
> > > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mas->offset =
=3D=3D wr_mas.node_end) ||
> > > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (node_size =3D=3D w=
r_mas.node_end &&
> > > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 wr_mas.offset=
_end - mas->offset =3D=3D 1))
> > > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
> >=20
> > I will add this to v2 as well, or something similar.
> >=20
> > > > > >=20
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 /* Potential spanning rebalance coll=
apsing a node, use worst-case */
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 if (node_size=C2=A0 - 1 <=3D mt_min_=
slots[wr_mas.type])
> > > > > > @@ -5590,7 +5592,6 @@ int mas_preallocate(struct ma_state *mas,=
 void *entry, gfp_t gfp)
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 if (likely(!mas_is_err(mas)))
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
> > > > > >=20
> > > > > > -=C2=A0=C2=A0=C2=A0 mas_set_alloc_req(mas, 0);
> >=20
> > Why did you drop this?  It seems like a worth while cleanup on failure.
> Because we will clear it in mas_node_count_gfp()->mas_alloc_nodes().

On failure we set the alloc request to the remainder of what was not
allocated.

> >=20
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 ret =3D xa_err(mas->node);
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 mas_reset(mas);
> > > > > >   =C2=A0=C2=A0=C2=A0=C2=A0 mas_destroy(mas);
> > > > > >=20
> > > > > >=20
> > > > > > >=20
> > > > > > >=20
> > > > > > > Regards
> > > > > > > Yin, Fengwei
> > > > > > >=20
> > > > > > > >=20
> > > > > > > > [1] https://lore.kernel.org/linux-mm/202305061457.ac15990c-=
yujie.liu@intel.com/
> > > > > > > >=20
> > > > > > > > Liam R. Howlett (14):
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Add benchmarking for mas_for_eac=
h
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Add benchmarking for mas_prev()
> > > > > > > >   =C2=A0=C2=A0 mm: Move unmap_vmas() declaration to interna=
l header
> > > > > > > >   =C2=A0=C2=A0 mm: Change do_vmi_align_munmap() side tree i=
ndex
> > > > > > > >   =C2=A0=C2=A0 mm: Remove prev check from do_vmi_align_munm=
ap()
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Introduce __mas_set_range()
> > > > > > > >   =C2=A0=C2=A0 mm: Remove re-walk from mmap_region()
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Re-introduce entry to mas_preall=
ocate() arguments
> > > > > > > >   =C2=A0=C2=A0 mm: Use vma_iter_clear_gfp() in nommu
> > > > > > > >   =C2=A0=C2=A0 mm: Set up vma iterator for vma_iter_preallo=
c() calls
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Move mas_wr_end_piv() below mas_=
wr_extend_null()
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Update mas_preallocate() testing
> > > > > > > >   =C2=A0=C2=A0 maple_tree: Refine mas_preallocate() node ca=
lculations
> > > > > > > >   =C2=A0=C2=A0 mm/mmap: Change vma iteration order in do_vm=
i_align_munmap()
> > > > > > > >=20
> > > > > > > >   =C2=A0 fs/exec.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 1 +
> > > > > > > >   =C2=A0 include/linux/maple_tree.h=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 |=C2=A0 23 ++++-
> > > > > > > >   =C2=A0 include/linux/mm.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 4 -
> > > > > > > >   =C2=A0 lib/maple_tree.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 78 =
++++++++++----
> > > > > > > >   =C2=A0 lib/test_maple_tree.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 74 +++++++++++++
> > > > > > > >   =C2=A0 mm/internal.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 |=C2=A0 40 ++++++--
> > > > > > > >   =C2=A0 mm/memory.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 |=C2=A0 16 ++-
> > > > > > > >   =C2=A0 mm/mmap.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0 | 171 ++++++++++++++++---------------
> > > > > > > >   =C2=A0 mm/nommu.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 |=C2=A0 45 ++++----
> > > > > > > >   =C2=A0 tools/testing/radix-tree/maple.c |=C2=A0 59 ++++++=
-----
> > > > > > > >   =C2=A0 10 files changed, 331 insertions(+), 180 deletions=
(-)
> > > > > > > >=20