linux-kernel - Re: [PATCH v3 07/11] mm: vmalloc: Offload free_vmap_area

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Date: Thu, 11 Jan 2024 16:54:48 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Dave Chinner <david@...morbit.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <willy@...radead.org>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v3 07/11] mm: vmalloc: Offload free_vmap_area_lock lock

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@...il.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.

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.

Thanks!

--
Uladzislau Rezki