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Date: Tue, 20 Apr 2021 15:16:25 +0800
From: Feng Tang <feng.tang@...el.com>
To: Michal Hocko <mhocko@...e.com>,
Dave Hansen <dave.hansen@...el.com>,
Ben Widawsky <ben.widawsky@...el.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Mike Kravetz <mike.kravetz@...cle.com>,
Randy Dunlap <rdunlap@...radead.org>,
Vlastimil Babka <vbabka@...e.cz>,
Dave Hansen <dave.hansen@...el.com>,
Ben Widawsky <ben.widawsky@...el.com>,
Andi Kleen <ak@...ux.intel.com>,
Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v4 03/13] mm/mempolicy: Add MPOL_PREFERRED_MANY for
multiple preferred nodes
On Wed, Apr 14, 2021 at 02:50:53PM +0200, Michal Hocko wrote:
> On Wed 17-03-21 11:40:00, Feng Tang wrote:
> > From: Dave Hansen <dave.hansen@...ux.intel.com>
> >
> > MPOL_PREFERRED honors only a single node set in the nodemask. Add the
> > bare define for a new mode which will allow more than one.
> >
> > The patch does all the plumbing without actually adding the new policy
> > type.
> >
> > v2:
> > Plumb most MPOL_PREFERRED_MANY without exposing UAPI (Ben)
> > Fixes for checkpatch (Ben)
> >
> > Link: https://lore.kernel.org/r/20200630212517.308045-4-ben.widawsky@intel.com
> > Co-developed-by: Ben Widawsky <ben.widawsky@...el.com>
> > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> > Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > ---
> > mm/mempolicy.c | 46 ++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 40 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 2b1e0e4..1228d8e 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -31,6 +31,9 @@
> > * but useful to set in a VMA when you have a non default
> > * process policy.
> > *
> > + * preferred many Try a set of nodes first before normal fallback. This is
> > + * similar to preferred without the special case.
> > + *
> > * default Allocate on the local node first, or when on a VMA
> > * use the process policy. This is what Linux always did
> > * in a NUMA aware kernel and still does by, ahem, default.
> > @@ -105,6 +108,8 @@
> >
> > #include "internal.h"
> >
> > +#define MPOL_PREFERRED_MANY MPOL_MAX
> > +
> > /* Internal flags */
> > #define MPOL_MF_DISCONTIG_OK (MPOL_MF_INTERNAL << 0) /* Skip checks for continuous vmas */
> > #define MPOL_MF_INVERT (MPOL_MF_INTERNAL << 1) /* Invert check for nodemask */
> > @@ -175,7 +180,7 @@ struct mempolicy *get_task_policy(struct task_struct *p)
> > static const struct mempolicy_operations {
> > int (*create)(struct mempolicy *pol, const nodemask_t *nodes);
> > void (*rebind)(struct mempolicy *pol, const nodemask_t *nodes);
> > -} mpol_ops[MPOL_MAX];
> > +} mpol_ops[MPOL_MAX + 1];
> >
> > static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
> > {
> > @@ -415,7 +420,7 @@ void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new)
> > mmap_write_unlock(mm);
> > }
> >
> > -static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
> > +static const struct mempolicy_operations mpol_ops[MPOL_MAX + 1] = {
> > [MPOL_DEFAULT] = {
> > .rebind = mpol_rebind_default,
> > },
> > @@ -432,6 +437,10 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
> > .rebind = mpol_rebind_nodemask,
> > },
> > /* [MPOL_LOCAL] - see mpol_new() */
> > + [MPOL_PREFERRED_MANY] = {
> > + .create = NULL,
> > + .rebind = NULL,
> > + },
> > };
>
> I do get that you wanted to keep MPOL_PREFERRED_MANY unaccessible for
> the userspace but wouldn't it be much easier to simply check in two
> syscall entries rather than playing thise MAX+1 games which make the
> review more complicated than necessary?
I will check this way, and currently the user input paramter
handling are quite complex.
Also the sanity check in kernel_mbind() and kernel_set_mempolicy()
are almost identical, which can be unified.
> >
> > static int migrate_page_add(struct page *page, struct list_head *pagelist,
> > @@ -924,6 +933,9 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
> > case MPOL_INTERLEAVE:
> > *nodes = p->v.nodes;
> > break;
> > + case MPOL_PREFERRED_MANY:
> > + *nodes = p->v.preferred_nodes;
> > + break;
> > case MPOL_PREFERRED:
> > if (!(p->flags & MPOL_F_LOCAL))
> > *nodes = p->v.preferred_nodes;
>
> Why those two do a slightly different thing? Is this because unlike
> MPOL_PREFERRED it can never have MPOL_F_LOCAL cleared? If that is the
> case I would still stick the two together and use the same code for
> both to make the code easier to follow. Now that both use the same
> nodemask it should really be just about syscall inputs sanitization and
> to keep the original behavior for MPOL_PREFERRED.
>
> [...]
Our intention is to make MPOL_PREFERRED_MANY be similar to
MPOL_PREFERRED, except it perfers multiple nodes. So will try to
achieve this in following version.
Also for MPOL_LOCAL and MPOL_PREFERRED, current code logic is
turning 'MPOL_LOCAL' to 'MPOL_PREFERRED' with MPOL_F_LOCAL set.
I don't understand why not use the other way around, that
turning MPOL_PREFERRED with empty nodemask to MPOL_LOCAL, which
looks more logical.
Thanks,
Feng
> > @@ -2072,6 +2087,9 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
> > task_lock(current);
> > mempolicy = current->mempolicy;
> > switch (mempolicy->mode) {
> > + case MPOL_PREFERRED_MANY:
> > + *mask = mempolicy->v.preferred_nodes;
> > + break;
> > case MPOL_PREFERRED:
> > if (mempolicy->flags & MPOL_F_LOCAL)
> > nid = numa_node_id();
>
> Same here
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