Re: [RFC PATCH 04/39] mm: mempolicy: Refactor out policy_node_nodemask()

Gregory Price
2024-09-11T16:46:52Z

On Tue, Sep 10, 2024 at 11:43:35PM +0000, Ackerley Tng wrote:
> This was refactored out of huge_node().
>
> huge_node()'s interpretation of vma for order assumes the
> hugetlb-specific storage of the hstate information in the
> inode. policy_node_nodemask() does not assume that, and can be used
> more generically.
>
> This refactoring also enforces that nid default to the current node
> id, which was not previously enforced.
>
> alloc_pages_mpol_noprof() is the last remaining direct user of
> policy_nodemask(). All its callers begin with nid being the current
> node id as well. More refactoring is required for to simplify that.
>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>

Reviewed-by: Gregory Price <gourry@gourry.net>

> +/**
> + * policy_node_nodemask(@mpol, @gfp_flags, @ilx, @nodemask)
> + * @mpol: the memory policy to interpret. Reference must be taken.
> + * @gfp_flags: for this request
> + * @ilx: interleave index, for use only when MPOL_INTERLEAVE or
> + * MPOL_WEIGHTED_INTERLEAVE
> + * @nodemask: (output) pointer to nodemask pointer for 'bind' and 'prefer-many'
> + * policy
> + *
> + * Returns a nid suitable for a page allocation and a pointer. If the effective
> + * policy is 'bind' or 'prefer-many', returns a pointer to the mempolicy's
> + * @nodemask for filtering the zonelist.

Technically it's possible for nid to contain MAX_NUMNODES upon return
if weighted interleave is used and the nodemask is somehow invalid
(contains no nodes, including the local node). I would expect this to
be indicative of a larger problem (i.e. should functionally never happen).

Now that I'm looking at it, it's possible the weighted interleave path
should default to returning numa_node_id() if node == MAX_NUMNODES, which
would not require any changes to this patch.

> + */
> +int policy_node_nodemask(struct mempolicy *mpol, gfp_t gfp_flags,
> + pgoff_t ilx, nodemask_t **nodemask)
> +{
> + int nid = numa_node_id();
> + *nodemask = policy_nodemask(gfp_flags, mpol, ilx, &nid);
> + return nid;
> +}
> +
> #ifdef CONFIG_HUGETLBFS
> /*
> * huge_node(@vma, @addr, @gfp_flags, @mpol)