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Date:   Thu, 12 Oct 2023 10:52:51 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Peng Zhang <zhangpeng.00@bytedance.com>
Cc:     maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        jason.sim@samsung.com, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] maple_tree: Add GFP_KERNEL to allocations in
 mas_expected_entries()
Message-ID: <20231012145251.n54lwp74gmdlympc@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        jason.sim@samsung.com, Andrew Morton <akpm@linux-foundation.org>
References: <20231010141737.1592866-1-Liam.Howlett@oracle.com>
 <14679c1d-463c-4dfb-8ccb-8b58c9e36c36@bytedance.com>
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* Peng Zhang <zhangpeng.00@bytedance.com> [231011 22:52]:
>=20
>=20
> =E5=9C=A8 2023/10/10 22:17, Liam R. Howlett =E5=86=99=E9=81=93:
> > Users complained about OOM errors during fork without triggering
> > compaction.  This can be fixed by modifying the flags used in
> > mas_expected_entries() so that the compaction will be triggered in low
> > memory situations.  Since mas_expected_entries() is only used during
> > fork, the extra argument does not need to be passed through.
> >=20
> > Additionally, the testing in the maple tree fork testing needed to be
> > altered to use the correct locking type so that allocations would not
> > trigger sleeping and thus failures in the testing.  The additional
> > locking change requires rwsem support additions to the tools/ directory
> > through the use of pthreads pthread_rwlock_t.  With this change
> > test_maple_tree works in userspace, as a module, and in-kernel.
> >=20
> > Users may notice that the system gave up early on attempting to start
> > new processes instead of attempting to reclaim memory.
> You still haven't updated check_forking() and bench_forking().
> It will still produce the same error as [1].

This did not show up on my testing, I will pull the bots config as I
must be missing something in there.

Thanks.

>=20
> [1] https://lore.kernel.org/oe-lkp/202309242123.7ebe65b5-oliver.sang@inte=
l.com/
> >=20
> > Link: https://lkml.kernel.org/r/20230915093243epcms1p46fa00bbac1ab7b7dc=
a94acb66c44c456@epcms1p4
> > Fixes: 54a611b60590 ("Maple Tree: add new data structure")
> > Cc: <stable@vger.kernel.org>
> > Cc: jason.sim@samsung.com
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> > ---
> >   lib/maple_tree.c            |  2 +-
> >   lib/test_maple_tree.c       | 13 ++++++++----
> >   tools/include/linux/rwsem.h | 40 ++++++++++++++++++++++++++++++++++++=
+
> >   3 files changed, 50 insertions(+), 5 deletions(-)
> >   create mode 100644 tools/include/linux/rwsem.h
> >=20
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index 0e00a84e8e8f..bb24d84a4922 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -5627,7 +5627,7 @@ int mas_expected_entries(struct ma_state *mas, un=
signed long nr_entries)
> >   	/* Internal nodes */
> >   	nr_nodes +=3D DIV_ROUND_UP(nr_nodes, nonleaf_cap);
> >   	/* Add working room for split (2 nodes) + new parents */
> > -	mas_node_count(mas, nr_nodes + 3);
> > +	mas_node_count_gfp(mas, nr_nodes + 3, GFP_KERNEL);
> >   	/* Detect if allocations run out */
> >   	mas->mas_flags |=3D MA_STATE_PREALLOC;
> > diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
> > index 06959165e2f9..204743bc161c 100644
> > --- a/lib/test_maple_tree.c
> > +++ b/lib/test_maple_tree.c
> > @@ -9,6 +9,7 @@
> >   #include <linux/maple_tree.h>
> >   #include <linux/module.h>
> > +#include <linux/rwsem.h>
> >   #define MTREE_ALLOC_MAX 0x2000000000000Ul
> >   #define CONFIG_MAPLE_SEARCH
> > @@ -2616,6 +2617,10 @@ static noinline void __init check_dup_gaps(struc=
t maple_tree *mt,
> >   	void *tmp;
> >   	MA_STATE(mas, mt, 0, 0);
> >   	MA_STATE(newmas, &newmt, 0, 0);
> > +	struct rw_semaphore newmt_lock;
> > +
> > +	init_rwsem(&newmt_lock);
> > +	mt_set_external_lock(&newmt, &newmt_lock);
> >   	if (!zero_start)
> >   		i =3D 1;
> > @@ -2625,9 +2630,9 @@ static noinline void __init check_dup_gaps(struct=
 maple_tree *mt,
> >   		mtree_store_range(mt, i*10, (i+1)*10 - gap,
> >   				  xa_mk_value(i), GFP_KERNEL);
> > -	mt_init_flags(&newmt, MT_FLAGS_ALLOC_RANGE);
> > +	mt_init_flags(&newmt, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN);
> >   	mt_set_non_kernel(99999);
> > -	mas_lock(&newmas);
> > +	down_write(&newmt_lock);
> >   	ret =3D mas_expected_entries(&newmas, nr_entries);
> >   	mt_set_non_kernel(0);
> >   	MT_BUG_ON(mt, ret !=3D 0);
> > @@ -2640,9 +2645,9 @@ static noinline void __init check_dup_gaps(struct=
 maple_tree *mt,
> >   	}
> >   	rcu_read_unlock();
> >   	mas_destroy(&newmas);
> > -	mas_unlock(&newmas);
> > -	mtree_destroy(&newmt);
> > +	__mt_destroy(&newmt);
> > +	up_write(&newmt_lock);
> >   }
> >   /* Duplicate many sizes of trees.  Mainly to test expected entry valu=
es */
> > diff --git a/tools/include/linux/rwsem.h b/tools/include/linux/rwsem.h
> > new file mode 100644
> > index 000000000000..83971b3cbfce
> > --- /dev/null
> > +++ b/tools/include/linux/rwsem.h
> > @@ -0,0 +1,40 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> > +#ifndef _TOOLS__RWSEM_H
> > +#define _TOOLS__RWSEM_H
> > +
> > +#include <pthread.h>
> > +
> > +struct rw_semaphore {
> > +	pthread_rwlock_t lock;
> > +};
> > +
> > +static inline int init_rwsem(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_init(&sem->lock, NULL);
> > +}
> > +
> > +static inline int exit_rwsem(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_destroy(&sem->lock);
> > +}
> > +
> > +static inline int down_read(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_rdlock(&sem->lock);
> > +}
> > +
> > +static inline int up_read(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_unlock(&sem->lock);
> > +}
> > +
> > +static inline int down_write(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_wrlock(&sem->lock);
> > +}
> > +
> > +static inline int up_write(struct rw_semaphore *sem)
> > +{
> > +	return pthread_rwlock_unlock(&sem->lock);
> > +}
> > +#endif /* _TOOLS_RWSEM_H */