From: Gregory Price <gregory.price@memverge.com>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Gregory Price <gourry.memverge@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-api@vger.kernel.org, corbet@lwn.net,
akpm@linux-foundation.org, honggyu.kim@sk.com, rakie.kim@sk.com,
hyeongtak.ji@sk.com, mhocko@kernel.org, vtavarespetr@micron.com,
jgroves@micron.com, ravis.opensrc@micron.com,
sthanneeru@micron.com, emirakhur@micron.com, Hasan.Maruf@amd.com,
seungjun.ha@samsung.com, hannes@cmpxchg.org,
dan.j.williams@intel.com,
Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Subject: Re: [PATCH v4 3/3] mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving
Date: Wed, 31 Jan 2024 11:35:53 -0500 [thread overview]
Message-ID: <Zbp26WZBkzhpLTLV@memverge.com> (raw)
In-Reply-To: <87y1c5g8qw.fsf@yhuang6-desk2.ccr.corp.intel.com>
On Wed, Jan 31, 2024 at 05:19:51PM +0800, Huang, Ying wrote:
> Gregory Price <gregory.price@memverge.com> writes:
>
> > On Wed, Jan 31, 2024 at 02:43:12PM +0800, Huang, Ying wrote:
> >> Gregory Price <gourry.memverge@gmail.com> writes:
> >> >
> >> > +static unsigned int weighted_interleave_nodes(struct mempolicy *policy)
> >> > +{
> >> > + unsigned int node = current->il_prev;
> >> > +
> >> > + if (!current->il_weight || !node_isset(node, policy->nodes)) {
> >> > + node = next_node_in(node, policy->nodes);
> >> > + /* can only happen if nodemask is being rebound */
> >> > + if (node == MAX_NUMNODES)
> >> > + return node;
> >>
> >> I feel a little unsafe to read policy->nodes at same time of writing in
> >> rebound. Is it better to use a seqlock to guarantee its consistency?
> >> It's unnecessary to be a part of this series though.
> >>
> >
> > I think this is handled already? It is definitely an explicit race
> > condition that is documented elsewhere:
> >
> > /*
> > * mpol_rebind_policy - Migrate a policy to a different set of nodes
> > *
> > * Per-vma policies are protected by mmap_lock. Allocations using per-task
> > * policies are protected by task->mems_allowed_seq to prevent a premature
> > * OOM/allocation failure due to parallel nodemask modification.
> > */
>
> Thanks for pointing this out!
>
> If we use task->mems_allowed_seq reader side in
> weighted_interleave_nodes() we can guarantee the consistency of
> policy->nodes. That may be not deserved, because it's not a big deal to
> allocate 1 page in a wrong node.
>
> It makes more sense to do that in
> alloc_pages_bulk_array_weighted_interleave(), because a lot of pages may
> be allocated there.
>
That's probably worth just adding now, I'll do it and squash the style
updates into the branch. Sorry Andrew, I guess 1 last version is
inbound :]
I'll pick up the reviewed tags along the way.
~Gregory
next prev parent reply other threads:[~2024-01-31 16:36 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-30 18:20 [PATCH v4 0/3] mm/mempolicy: weighted interleave mempolicy and sysfs extension Gregory Price
2024-01-30 18:20 ` [PATCH v4 1/3] mm/mempolicy: implement the sysfs-based weighted_interleave interface Gregory Price
2024-01-30 18:20 ` [PATCH v4 2/3] mm/mempolicy: refactor a read-once mechanism into a function for re-use Gregory Price
2024-01-30 18:20 ` [PATCH v4 3/3] mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving Gregory Price
2024-01-31 5:12 ` Gregory Price
2024-01-31 6:43 ` Huang, Ying
2024-01-31 7:43 ` Gregory Price
2024-01-31 9:19 ` Huang, Ying
2024-01-31 16:35 ` Gregory Price [this message]
2024-01-31 17:29 ` Gregory Price
2024-02-01 1:55 ` Huang, Ying
2024-02-01 2:01 ` Gregory Price
2024-02-01 2:18 ` Gregory Price
2024-02-01 3:02 ` Huang, Ying
2024-02-01 3:10 ` Gregory Price
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