From: Uladzislau Rezki <urezki@gmail.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Uladzislau Rezki <urezki@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
"Theodore Y . Ts'o" <tytso@mit.edu>,
Matthew Wilcox <willy@infradead.org>,
Joel Fernandes <joel@joelfernandes.org>,
RCU <rcu@vger.kernel.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs
Date: Thu, 18 Jun 2020 19:56:23 +0200 [thread overview]
Message-ID: <20200618175623.GA14865@pc636> (raw)
In-Reply-To: <20200618173206.GS2723@paulmck-ThinkPad-P72>
On Thu, Jun 18, 2020 at 10:32:06AM -0700, Paul E. McKenney wrote:
> On Thu, Jun 18, 2020 at 07:25:04PM +0200, Uladzislau Rezki wrote:
> > > > + // Handle two first channels.
> > > > + for (i = 0; i < FREE_N_CHANNELS; i++) {
> > > > + for (; bkvhead[i]; bkvhead[i] = bnext) {
> > > > + bnext = bkvhead[i]->next;
> > > > + debug_rcu_bhead_unqueue(bkvhead[i]);
> > > > +
> > > > + rcu_lock_acquire(&rcu_callback_map);
> > > > + if (i == 0) { // kmalloc() / kfree().
> > > > + trace_rcu_invoke_kfree_bulk_callback(
> > > > + rcu_state.name, bkvhead[i]->nr_records,
> > > > + bkvhead[i]->records);
> > > > +
> > > > + kfree_bulk(bkvhead[i]->nr_records,
> > > > + bkvhead[i]->records);
> > > > + } else { // vmalloc() / vfree().
> > > > + for (j = 0; j < bkvhead[i]->nr_records; j++) {
> > > > + trace_rcu_invoke_kfree_callback(
> > > > + rcu_state.name,
> > > > + bkvhead[i]->records[j], 0);
> > > > +
> > > > + vfree(bkvhead[i]->records[j]);
> > > > + }
> > > > + }
> > > > + rcu_lock_release(&rcu_callback_map);
> > >
> > > Not an emergency, but did you look into replacing this "if" statement
> > > with an array of pointers to functions implementing the legs of the
> > > "if" statement? If nothing else, this would greatly reduced indentation.
> > >
> > >
> > > I am taking this as is, but if you have not already done so, could you
> > > please look into this for a follow-up patch?
> > >
> > I do not think it makes sense, because it would require to check each
> > pointer in the array, what can lead to many branching, i.e. "if-else"
> > instructions.
>
> Mightn't the compiler simply unroll the outer loop? Then the first
> unrolled iteration of that loop would contain the then-clause and
> the second unrolled iteration would contain the else-clause. At that
> point, there would be no checking, just direct calls.
>
> Or am I missing something?
>
If we mix pointers, then we can do free per pointer only. I mean in that
case we will not be able to use kfree_bulk() interface for freeing SLAB
memory and the code would converted to something like:
<snip>
while (nr_objects_in_array > 0) {
if (is_vmalloc_addr(array[X]))
vfree(array[X]);
else
kfree(array[X]);
}
<snip>
> > Paul, thank you to take it in!
>
> Thank you for persisting!
>
Welcome :)
--
Vlad Rezki
next prev parent reply other threads:[~2020-06-18 17:56 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-25 21:47 [PATCH v2 00/16] Introduce kvfree_rcu(1 or 2 arguments) Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 01/16] rcu/tree: Keep kfree_rcu() awake during lock contention Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 02/16] rcu/tree: Skip entry into the page allocator for PREEMPT_RT Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 03/16] rcu/tree: Repeat the monitor if any free channel is busy Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 04/16] rcu/tree: Make debug_objects logic independent of rcu_head Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 05/16] rcu/tree: Simplify KFREE_BULK_MAX_ENTR macro Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 06/16] rcu/tree: Move kfree_rcu_cpu locking/unlocking to separate functions Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 07/16] rcu/tree: Use static initializer for krc.lock Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 08/16] rcu/tree: cache specified number of objects Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs Uladzislau Rezki (Sony)
2020-06-17 23:46 ` Paul E. McKenney
2020-06-18 0:52 ` Matthew Wilcox
2020-06-18 3:18 ` Paul E. McKenney
2020-06-18 17:35 ` Uladzislau Rezki
2020-06-18 17:57 ` Paul E. McKenney
2020-06-18 18:34 ` Uladzislau Rezki
2020-06-18 19:03 ` Paul E. McKenney
2020-06-18 20:35 ` Uladzislau Rezki
2020-06-18 20:38 ` Matthew Wilcox
2020-06-18 21:17 ` Uladzislau Rezki
2020-06-18 21:34 ` Paul E. McKenney
2020-06-19 15:46 ` Uladzislau Rezki
2020-06-19 16:25 ` Paul E. McKenney
2020-06-22 19:04 ` Uladzislau Rezki
2020-06-22 19:53 ` Paul E. McKenney
2020-06-30 17:46 ` Uladzislau Rezki
2020-06-18 17:30 ` Uladzislau Rezki
2020-06-18 17:35 ` Matthew Wilcox
2020-06-18 20:03 ` Uladzislau Rezki
2020-06-18 17:25 ` Uladzislau Rezki
2020-06-18 17:32 ` Paul E. McKenney
2020-06-18 17:56 ` Uladzislau Rezki [this message]
2020-06-18 18:15 ` Matthew Wilcox
2020-06-18 18:23 ` Uladzislau Rezki
2020-06-18 18:37 ` Matthew Wilcox
2020-06-18 18:48 ` Uladzislau Rezki
2020-05-25 21:47 ` [PATCH v2 10/16] rcu/tiny: support vmalloc in tiny-RCU Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 11/16] rcu: Rename *_kfree_callback/*_kfree_rcu_offset/kfree_call_* Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 12/16] mm/list_lru.c: Rename kvfree_rcu() to local variant Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 13/16] rcu: Introduce 2 arg kvfree_rcu() interface Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 14/16] rcu: Support reclaim for head-less object Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 15/16] rcu: Introduce single argument kvfree_rcu() interface Uladzislau Rezki (Sony)
2020-05-25 21:48 ` [PATCH v2 16/16] lib/test_vmalloc.c: Add test cases for kvfree_rcu() Uladzislau Rezki (Sony)
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