From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Thomas Garnier <thgarnie@google.com>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC v1] mm: add the preempt check into alloc_vmap_area()
Date: Fri, 2 Mar 2018 15:34:52 -0800 [thread overview]
Message-ID: <20180302153452.748892bd70bb23b9cee23691@linux-foundation.org> (raw)
In-Reply-To: <20180227130643.GA12781@bombadil.infradead.org>
On Tue, 27 Feb 2018 05:06:43 -0800 Matthew Wilcox <willy@infradead.org> wrote:
> On Tue, Feb 27, 2018 at 11:22:59AM +0100, Uladzislau Rezki (Sony) wrote:
> > During finding a suitable hole in the vmap_area_list
> > there is an explicit rescheduling check for latency reduction.
> > We do it, since there are workloads which are sensitive for
> > long (more than 1 millisecond) preemption off scenario.
>
> I understand your problem, but this is a horrid solution. If it takes
> us a millisecond to find a suitable chunk of free address space, something
> is terribly wrong. On a 3GHz CPU, that's 3 million clock ticks!
Yup.
> I think our real problem is that we have no data structure that stores
> free VA space. We have the vmap_area which stores allocated space, but no
> data structure to store free space.
I wonder if we can reuse free_vmap_cache as a quick fix: if
need_resched(), point free_vmap_cache at the current rb_node, drop the
lock, cond_resched, goto retry?
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next prev parent reply other threads:[~2018-03-02 23:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 10:22 Uladzislau Rezki (Sony)
2018-02-27 13:06 ` Matthew Wilcox
2018-02-28 12:40 ` Uladzislau Rezki
2018-03-02 23:34 ` Andrew Morton [this message]
2018-03-03 21:18 ` Uladzislau Rezki
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