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@xxxxxxxxxxxxx>
> ---
> 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
