From: Uladzislau Rezki <urezki@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Uladzislau Rezki <urezki@gmail.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>, Baoquan He <bhe@redhat.com>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Subject: Re: [PATCH v3 07/11] mm: vmalloc: Offload free_vmap_area_lock lock
Date: Thu, 18 Jan 2024 19:15:13 +0100 [thread overview]
Message-ID: <Zalqsf5MiU7Q7ewN@pc636> (raw)
In-Reply-To: <Zab/Sm0FXjnNvseR@dread.disaster.area>
On Wed, Jan 17, 2024 at 09:12:26AM +1100, Dave Chinner wrote:
> On Fri, Jan 12, 2024 at 01:18:27PM +0100, Uladzislau Rezki wrote:
> > On Fri, Jan 12, 2024 at 07:37:36AM +1100, Dave Chinner wrote:
> > > On Thu, Jan 11, 2024 at 04:54:48PM +0100, Uladzislau Rezki wrote:
> > > > On Thu, Jan 11, 2024 at 08:02:16PM +1100, Dave Chinner wrote:
> > > > > On Tue, Jan 02, 2024 at 07:46:29PM +0100, Uladzislau Rezki (Sony) wrote:
> > > > > > Concurrent access to a global vmap space is a bottle-neck.
> > > > > > We can simulate a high contention by running a vmalloc test
> > > > > > suite.
> > > > > >
> > > > > > To address it, introduce an effective vmap node logic. Each
> > > > > > node behaves as independent entity. When a node is accessed
> > > > > > it serves a request directly(if possible) from its pool.
> > > > > >
> > > > > > This model has a size based pool for requests, i.e. pools are
> > > > > > serialized and populated based on object size and real demand.
> > > > > > A maximum object size that pool can handle is set to 256 pages.
> > > > > >
> > > > > > This technique reduces a pressure on the global vmap lock.
> > > > > >
> > > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > >
> > > > > Why not use a llist for this? That gets rid of the need for a
> > > > > new pool_lock altogether...
> > > > >
> > > > Initially i used the llist. I have changed it because i keep track
> > > > of objects per a pool to decay it later. I do not find these locks
> > > > as contented one therefore i did not think much.
> > >
> > > Ok. I've used llist and an atomic counter to track the list length
> > > in the past.
> > >
> > > But is the list length even necessary? It seems to me that it is
> > > only used by the shrinker to determine how many objects are on the
> > > lists for scanning, and I'm not sure that's entirely necessary given
> > > the way the current global shrinker works (i.e. completely unfair to
> > > low numbered nodes due to scan loop start bias).
> > >
> > I use the length to decay pools by certain percentage, currently it is
> > 25%, so i need to know number of objects. It is done in the purge path.
> > As for shrinker, once it hits us we drain pools entirely.
>
> Why does purge need to be different to shrinking?
>
> But, regardless, you can still use llist with an atomic counter to
> do this - there is no need for a spin lock at all.
>
As i pointed earlier, i will have a look at it.
> > > > Anyway, i will have a look at this to see if llist is easy to go with
> > > > or not. If so i will send out a separate patch.
> > >
> > > Sounds good, it was just something that crossed my mind given the
> > > pattern of "producer adds single items, consumer detaches entire
> > > list, processes it and reattaches remainder" is a perfect match for
> > > the llist structure.
> > >
> > The llist_del_first() has to be serialized. For this purpose a per-cpu
> > pool would work or kind of "in_use" atomic that protects concurrent
> > removing.
>
> So don't use llist_del_first().
>
> > If we detach entire llist, then we need to keep track of last node
> > to add it later as a "batch" to already existing/populated list.
>
> Why? I haven't see any need for ordering these lists which would
> requiring strict tail-add ordered semantics.
>
I mean the following:
1. first = llist_del_all(&example);
2. last = llist_reverse_order(first);
4. va = __llist_del_first(first);
/*
* "example" might not be empty, use the batch. Otherwise
* we loose the entries "example" pointed to.
*/
3. llist_add_batch(first, last, &example);
--
Uladzislau Rezki
next prev parent reply other threads:[~2024-01-18 18:15 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-02 18:46 [PATCH v3 00/11] Mitigate a vmap lock contention v3 Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 01/11] mm: vmalloc: Add va_alloc() helper Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 02/11] mm: vmalloc: Rename adjust_va_to_fit_type() function Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 03/11] mm: vmalloc: Move vmap_init_free_space() down in vmalloc.c Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 04/11] mm: vmalloc: Remove global vmap_area_root rb-tree Uladzislau Rezki (Sony)
2024-01-05 8:10 ` Wen Gu
2024-01-05 10:50 ` Uladzislau Rezki
2024-01-06 9:17 ` Wen Gu
2024-01-06 16:36 ` Uladzislau Rezki
2024-01-07 6:59 ` Hillf Danton
2024-01-08 7:45 ` Wen Gu
2024-01-08 18:37 ` Uladzislau Rezki
2024-01-16 23:25 ` Lorenzo Stoakes
2024-01-18 13:15 ` Uladzislau Rezki
2024-01-20 12:55 ` Lorenzo Stoakes
2024-01-22 17:44 ` Uladzislau Rezki
2024-01-02 18:46 ` [PATCH v3 05/11] mm/vmalloc: remove vmap_area_list Uladzislau Rezki (Sony)
2024-01-16 23:36 ` Lorenzo Stoakes
2024-01-02 18:46 ` [PATCH v3 06/11] mm: vmalloc: Remove global purge_vmap_area_root rb-tree Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 07/11] mm: vmalloc: Offload free_vmap_area_lock lock Uladzislau Rezki (Sony)
2024-01-03 11:08 ` Hillf Danton
2024-01-03 15:47 ` Uladzislau Rezki
2024-01-11 9:02 ` Dave Chinner
2024-01-11 15:54 ` Uladzislau Rezki
2024-01-11 20:37 ` Dave Chinner
2024-01-12 12:18 ` Uladzislau Rezki
2024-01-16 22:12 ` Dave Chinner
2024-01-18 18:15 ` Uladzislau Rezki [this message]
2024-02-08 0:25 ` Baoquan He
2024-02-08 13:57 ` Uladzislau Rezki
2024-02-28 9:48 ` Baoquan He
2024-02-28 10:39 ` Uladzislau Rezki
2024-02-28 12:26 ` Baoquan He
2024-03-22 18:21 ` Guenter Roeck
2024-03-22 19:03 ` Uladzislau Rezki
2024-03-22 20:53 ` Guenter Roeck
2024-01-02 18:46 ` [PATCH v3 08/11] mm: vmalloc: Support multiple nodes in vread_iter Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 09/11] mm: vmalloc: Support multiple nodes in vmallocinfo Uladzislau Rezki (Sony)
2024-01-02 18:46 ` [PATCH v3 10/11] mm: vmalloc: Set nr_nodes based on CPUs in a system Uladzislau Rezki (Sony)
2024-01-11 9:25 ` Dave Chinner
2024-01-15 19:09 ` Uladzislau Rezki
2024-01-16 22:06 ` Dave Chinner
2024-01-18 18:23 ` Uladzislau Rezki
2024-01-18 21:28 ` Dave Chinner
2024-01-19 10:32 ` Uladzislau Rezki
2024-01-02 18:46 ` [PATCH v3 11/11] mm: vmalloc: Add a shrinker to drain vmap pools Uladzislau Rezki (Sony)
2024-02-22 8:35 ` [PATCH v3 00/11] Mitigate a vmap lock contention v3 Uladzislau Rezki
2024-02-22 23:15 ` Pedro Falcato
2024-02-23 9:34 ` Uladzislau Rezki
2024-02-23 10:26 ` Baoquan He
2024-02-23 11:06 ` Uladzislau Rezki
2024-02-23 15:57 ` Baoquan He
2024-02-23 18:55 ` Uladzislau Rezki
2024-02-28 9:27 ` Baoquan He
2024-02-29 10:38 ` Uladzislau Rezki
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