Re: [PATCH v10 1/2] memory tier: dax/kmem: introduce an abstract layer for finding, allocating, and putting memory types

Ho-Ren (Jack) Chuang
2024-04-03T23:13:35Z

Hi Jonathan,

Thanks for your feedback. I will fix them (inlined) in the next V11.
No worries, it's never too late!

On Wed, Apr 3, 2024 at 9:52 AM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 2 Apr 2024 00:17:37 +0000
> "Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com> wrote:
>
> > Since different memory devices require finding, allocating, and putting
> > memory types, these common steps are abstracted in this patch,
> > enhancing the scalability and conciseness of the code.
> >
> > Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
> > Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
>
> Hi,
>
> I know this is a late entry to the discussion but a few comments inline.
> (sorry I didn't look earlier!)
>
> All opportunities to improve code complexity and readability as a result
> of your factoring out.
>
> Jonathan
>
>
> > ---
> > drivers/dax/kmem.c | 20 ++------------------
> > include/linux/memory-tiers.h | 13 +++++++++++++
> > mm/memory-tiers.c | 32 ++++++++++++++++++++++++++++++++
> > 3 files changed, 47 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> > index 42ee360cf4e3..01399e5b53b2 100644
> > --- a/drivers/dax/kmem.c
> > +++ b/drivers/dax/kmem.c
> > @@ -55,21 +55,10 @@ static LIST_HEAD(kmem_memory_types);
> >
> > static struct memory_dev_type *kmem_find_alloc_memory_type(int adist)
> > {
> > - bool found = false;
> > struct memory_dev_type *mtype;
> >
> > mutex_lock(&kmem_memory_type_lock);
> could use
>
> guard(mutex)(&kmem_memory_type_lock);
> return mt_find_alloc_memory_type(adist, &kmem_memory_types);
>

I will change it accordingly.

> I'm fine if you ignore this comment though as may be other functions in
> here that could take advantage of the cleanup.h stuff in a future patch.
>
> > - list_for_each_entry(mtype, &kmem_memory_types, list) {
> > - if (mtype->adistance == adist) {
> > - found = true;
> > - break;
> > - }
> > - }
> > - if (!found) {
> > - mtype = alloc_memory_type(adist);
> > - if (!IS_ERR(mtype))
> > - list_add(&mtype->list, &kmem_memory_types);
> > - }
> > + mtype = mt_find_alloc_memory_type(adist, &kmem_memory_types);
> > mutex_unlock(&kmem_memory_type_lock);
> >
> > return mtype;
>
> > diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> > index 69e781900082..a44c03c2ba3a 100644
> > --- a/include/linux/memory-tiers.h
> > +++ b/include/linux/memory-tiers.h
> > @@ -48,6 +48,9 @@ int mt_calc_adistance(int node, int *adist);
> > int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> > const char *source);
> > int mt_perf_to_adistance(struct access_coordinate *perf, int *adist);
> > +struct memory_dev_type *mt_find_alloc_memory_type(int adist,
> > + struct list_head *memory_types);
>
> That indent looks unusual. Align the start of struct with start of int.
>

I can make this aligned but it will show another warning:
"WARNING: line length of 131 exceeds 100 columns"
Is this ok?

> > +void mt_put_memory_types(struct list_head *memory_types);
> > #ifdef CONFIG_MIGRATION
> > int next_demotion_node(int node);
> > void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
> > @@ -136,5 +139,15 @@ static inline int mt_perf_to_adistance(struct access_coordinate *perf, int *adis
> > {
> > return -EIO;
> > }
> > +
> > +struct memory_dev_type *mt_find_alloc_memory_type(int adist, struct list_head *memory_types)
> > +{
> > + return NULL;
> > +}
> > +
> > +void mt_put_memory_types(struct list_head *memory_types)
> > +{
> > +
> No blank line needed here.

Will fix.

> > +}
> > #endif /* CONFIG_NUMA */
> > #endif /* _LINUX_MEMORY_TIERS_H */
> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > index 0537664620e5..974af10cfdd8 100644
> > --- a/mm/memory-tiers.c
> > +++ b/mm/memory-tiers.c
> > @@ -623,6 +623,38 @@ void clear_node_memory_type(int node, struct memory_dev_type *memtype)
> > }
> > EXPORT_SYMBOL_GPL(clear_node_memory_type);
> >
> > +struct memory_dev_type *mt_find_alloc_memory_type(int adist, struct list_head *memory_types)
>
> Breaking this out as a separate function provides opportunity to improve it.
> Maybe a follow up patch makes sense given it would no longer be a straight
> forward code move. However in my view it would be simple enough to be obvious
> even within this patch.
>

I will just keep this as is for now to minimize the changes aka mistakes.

> > +{
> > + bool found = false;
> > + struct memory_dev_type *mtype;
> > +
> > + list_for_each_entry(mtype, memory_types, list) {
> > + if (mtype->adistance == adist) {
> > + found = true;
>
> Why not return here?
> return mtype;
>

Yes, I can return here. I will do that and take care of the ptr
returning at this point.

> > + break;
> > + }
> > + }
> > + if (!found) {
>
> If returning above, no need for found variable - just do this unconditionally.
> + I suggest you flip logic for simpler to follow code flow.
> It's more code but I think a bit easier to read as error handling is
> out of the main simple flow.
>
> mtype = alloc_memory_type(adist);
> if (IS_ERR(mtype))
> return mtype;
>
> list_add(&mtype->list, memory_types);
>
> return mtype;
>

Good idea! I will change it accordingly.

> > + mtype = alloc_memory_type(adist);
> > + if (!IS_ERR(mtype))
> > + list_add(&mtype->list, memory_types);
> > + }
> > +
> > + return mtype;
> > +}
> > +EXPORT_SYMBOL_GPL(mt_find_alloc_memory_type);
> > +
> > +void mt_put_memory_types(struct list_head *memory_types)
> > +{
> > + struct memory_dev_type *mtype, *mtn;
> > +
> > + list_for_each_entry_safe(mtype, mtn, memory_types, list) {
> > + list_del(&mtype->list);
> > + put_memory_type(mtype);
> > + }
> > +}
> > +EXPORT_SYMBOL_GPL(mt_put_memory_types);
> > +
> > static void dump_hmem_attrs(struct access_coordinate *coord, const char *prefix)
> > {
> > pr_info(
>

--
Best regards,
Ho-Ren (Jack) Chuang
莊賀任