From: Michal Hocko <mhocko@suse.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: akpm@linux-foundation.org, bwidawsk@kernel.org,
dave.hansen@linux.intel.com, feng.tang@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: mempolicy: fix policy_nodemask() for MPOL_PREFERRED_MANY case
Date: Mon, 1 Aug 2022 11:06:14 +0200 [thread overview]
Message-ID: <YueXhmiFcI8iw3OI@dhcp22.suse.cz> (raw)
In-Reply-To: <20220801084207.39086-1-songmuchun@bytedance.com>
On Mon 01-08-22 16:42:07, Muchun Song wrote:
> policy_nodemask() is supposed to be returned a nodemask representing a mempolicy
> for filtering nodes for page allocation, which is a hard restriction (see the user
> of allowed_mems_nr() in hugetlb.c). However, MPOL_PREFERRED_MANY is a preferred
> mode not a hard restriction. Now it breaks the user of HugeTLB. Remove it from
> policy_nodemask() to fix it, which will not affect current users of policy_nodemask()
> since all of the users already have handled the case of MPOL_PREFERRED_MANY before
> calling it. BTW, it is found by code inspection.
I am not sure this is the right fix. It is quite true that
policy_nodemask is a tricky function to use. It pretends to have a
higher level logic but all existing users are expected to be policy
aware and they special case allocation for each policy. That would mean
that hugetlb should do the same.
I haven't checked the actual behavior implications for hugetlb here. Is
MPOL_PREFERRED_MANY even supported for hugetlb? Does this change make it
work? From a quick look this just ignores MPOL_PREFERRED_MANY
completely.
> Fixes: b27abaccf8e8 ("mm/mempolicy: add MPOL_PREFERRED_MANY for multiple preferred nodes")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/mempolicy.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 6c27acb6cd63..4deec7e598c6 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1845,9 +1845,6 @@ nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy)
> cpuset_nodemask_valid_mems_allowed(&policy->nodes))
> return &policy->nodes;
>
> - if (mode == MPOL_PREFERRED_MANY)
> - return &policy->nodes;
> -
> return NULL;
> }
>
> --
> 2.11.0
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2022-08-01 9:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-01 8:42 [PATCH] mm: mempolicy: fix policy_nodemask() for MPOL_PREFERRED_MANY case Muchun Song
2022-08-01 9:06 ` Michal Hocko [this message]
2022-08-01 9:26 ` Feng Tang
2022-08-02 3:42 ` Muchun Song
2022-08-02 5:52 ` Feng Tang
2022-08-02 6:40 ` Muchun Song
2022-08-02 7:39 ` Feng Tang
2022-08-02 9:02 ` Michal Hocko
2022-08-03 6:41 ` Feng Tang
2022-08-03 7:36 ` Michal Hocko
2022-08-03 17:14 ` Feng Tang
2022-08-03 11:28 ` Michal Hocko
2022-08-03 20:43 ` Feng Tang
2022-08-03 12:56 ` Michal Hocko
2022-08-03 21:08 ` Feng Tang
2022-08-03 13:21 ` Michal Hocko
2022-08-04 8:27 ` Feng Tang
2022-08-04 10:43 ` Michal Hocko
2022-08-04 13:03 ` [PATCH] mm/hugetlb: add dedicated func to get 'allowed' nodemask for current process Feng Tang
2022-08-04 13:36 ` Michal Hocko
2022-08-04 22:37 ` Andrew Morton
2022-08-05 0:06 ` Feng Tang
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