From: Matthew Wilcox <willy@infradead.org>
To: Christoph Lameter <cl@gentwo.de>
Cc: Xunlei Pang <xlpang@linux.alibaba.com>,
Vlastimil Babka <vbabka@suse.cz>,
Wen Yang <wenyang@linux.alibaba.com>,
Roman Gushchin <guro@fb.com>, Pekka Enberg <penberg@gmail.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH v2 3/3] mm/slub: Use percpu partial free counter
Date: Wed, 3 Mar 2021 20:16:49 +0000 [thread overview]
Message-ID: <20210303201649.GF2723601@casper.infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2103032032070.897408@gentwo.de>
On Wed, Mar 03, 2021 at 08:55:48PM +0100, Christoph Lameter wrote:
> On Wed, 3 Mar 2021, Matthew Wilcox wrote:
>
> > > Can this be allocated in an interrupt context?
> > >
> > > And I am not sure how local_t relates to that? Percpu counters can be used
> > > in an interrupt context without the overhead of the address calculations
> > > that are required by a local_t.
> >
> > As I understand the patch, this counts the number of partially free slabs.
> > So if we start to free an object from a completely full slab in process
> > context, as "load x, add one to x, store x" and take an interrupt
> > between loading x and adding one to x, that interrupt handler might
> > free a different object from another completely full slab. that would
> > also load the same x, add one to it and store x, but then the process
> > context would add one to the old x, overwriting the updated value from
> > interrupt context.
>
> this_cpu operations are "atomic" vs. preemption but on some platforms not
> vs interrupts. That could be an issue in kmem_cache_free(). This would
> need a modification to the relevant this_cpu ops so that interrupts are
> disabled on those platforms.
Hmmmm ... re-reading the documentation, it says that this_cpu_x is
atomic against interrupts:
These operations can be used without worrying about
preemption and interrupts::
[...]
this_cpu_add(pcp, val)
this_cpu_inc(pcp)
...
next prev parent reply other threads:[~2021-03-04 0:03 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 12:17 [PATCH v2 0/3] mm/slub: Fix count_partial() problem Xunlei Pang
2020-08-10 12:17 ` [PATCH v2 1/3] mm/slub: Introduce two counters for partial objects Xunlei Pang
2020-08-10 12:17 ` [PATCH v2 2/3] mm/slub: Get rid of count_partial() Xunlei Pang
2020-08-10 12:17 ` [PATCH v2 3/3] mm/slub: Use percpu partial free counter Xunlei Pang
2021-03-02 5:56 ` Shu Ming
2021-03-02 9:14 ` Christoph Lameter
2021-03-03 13:46 ` Xunlei Pang
2021-03-03 14:26 ` Matthew Wilcox
2021-03-03 19:15 ` Christoph Lameter
2021-03-03 19:30 ` Matthew Wilcox
2021-03-03 19:55 ` Christoph Lameter
2021-03-03 20:16 ` Matthew Wilcox [this message]
2020-08-20 14:02 ` [PATCH v2 0/3] mm/slub: Fix count_partial() problem Pekka Enberg
2020-08-24 10:04 ` xunlei
2021-03-01 10:31 ` Shu Ming
2021-03-03 13:34 ` Xunlei Pang
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