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SubjectRe: [PATCH v1 2/6] rcu: introduce kvfree_rcu() interface
On Mon, Mar 16, 2020 at 11:45:39AM -0400, Joel Fernandes wrote:
> On Sun, Mar 15, 2020 at 07:18:36PM +0100, Uladzislau Rezki (Sony) wrote:
> > kvfree_rcu() can deal with an allocated memory that is obtained
> > via kvmalloc(). It can return two types of allocated memory or
> > "pointers", one can belong to regular SLAB allocator and another
> > one can be vmalloc one. It depends on requested size and memory
> > pressure.
> >
> > Based on that, two streams are split, thus if a pointer belongs
> > to vmalloc allocator it is queued to the list, otherwise SLAB
> > one is queued into "bulk array" for further processing.
> >
> > The main reason of such splitting is:
> > a) to distinguish kmalloc()/vmalloc() ptrs;
> > b) there is no vmalloc_bulk() interface.
> >
> > As of now we have list_lru.c user that needs such interface,
> > also there will be new comers. Apart of that it is preparation
> > to have a head-less variant later.
> >
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > ---
> > include/linux/rcupdate.h | 9 +++++++++
> > kernel/rcu/tiny.c | 3 ++-
> > kernel/rcu/tree.c | 17 ++++++++++++-----
> > 3 files changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 2be97a83f266..bb270221dbdc 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -845,6 +845,15 @@ do { \
> > __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
> > } while (0)
> >
> > +/**
> > + * kvfree_rcu() - kvfree an object after a grace period.
> > + * @ptr: pointer to kvfree
> > + * @rhf: the name of the struct rcu_head within the type of @ptr.
> > + *
> > + * Same as kfree_rcu(), just simple alias.
> > + */
> > +#define kvfree_rcu(ptr, rhf) kfree_rcu(ptr, rhf)
> > +
> > /*
> > * Place this after a lock-acquisition primitive to guarantee that
> > * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
> > diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> > index dd572ce7c747..4b99f7b88bee 100644
> > --- a/kernel/rcu/tiny.c
> > +++ b/kernel/rcu/tiny.c
> > @@ -23,6 +23,7 @@
> > #include <linux/cpu.h>
> > #include <linux/prefetch.h>
> > #include <linux/slab.h>
> > +#include <linux/mm.h>
> >
> > #include "rcu.h"
> >
> > @@ -86,7 +87,7 @@ static inline bool rcu_reclaim_tiny(struct rcu_head *head)
> > rcu_lock_acquire(&rcu_callback_map);
> > if (__is_kfree_rcu_offset(offset)) {
> > trace_rcu_invoke_kfree_callback("", head, offset);
> > - kfree((void *)head - offset);
> > + kvfree((void *)head - offset);
> > rcu_lock_release(&rcu_callback_map);
> > return true;
> > }
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 2f4c91a3713a..1c0a73616872 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -2899,9 +2899,9 @@ static void kfree_rcu_work(struct work_struct *work)
> > }
> >
> > /*
> > - * Emergency case only. It can happen under low memory
> > - * condition when an allocation gets failed, so the "bulk"
> > - * path can not be temporary maintained.
> > + * vmalloc() pointers end up here also emergency case. It can
>
> Suggest rephrase for clarity:
>
> nit: We can end up here either with 1) vmalloc() pointers or 2) low on memory
> and could not allocate a bulk array.
>
Let's go with your suggestion. I see that you took patches to your tree.
Could you please update it on your own? Otherwise i can send out V2, so
please let me know.

Thanks for the comments!

--
Vlad Rezki

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