From: David Hildenbrand <david@redhat.com>
To: Michael Ellerman <mpe@ellerman.id.au>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Thiago Jung Bauermann <bauerman@linux.ibm.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
Oliver O'Halloran <oohall@gmail.com>,
Alexey Kardashevskiy <aik@ozlabs.ru>,
"Enrico Weigelt, metux IT consult" <info@metux.net>,
Thomas Gleixner <tglx@linutronix.de>,
Allison Randal <allison@lohutok.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Arun KS <arunks@codeaurora.org>, Todd Kjos <tkjos@google.com>,
Christian Brauner <christian@brauner.io>,
Gao Xiang <xiang@kernel.org>,
Greg Hackmann <ghackmann@google.com>,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH v1 08/12] powerpc/pseries: CMM: Implement balloon compaction
Date: Tue, 12 Nov 2019 12:12:33 +0100 [thread overview]
Message-ID: <8e46b1c5-f52b-0155-4d4f-e3bbdea95384@redhat.com> (raw)
In-Reply-To: <87blth2wyk.fsf@mpe.ellerman.id.au>
On 12.11.19 11:46, Michael Ellerman wrote:
> David Hildenbrand <david@redhat.com> writes:
>> On 31.10.19 15:29, David Hildenbrand wrote:
>>> We can now get rid of the cmm_lock and completely rely on the balloon
>>> compaction internals, which now also manage the page list and the lock.
> ...
>>> +
>>> +static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
>>> + struct page *newpage, struct page *page,
>>> + enum migrate_mode mode)
>>> +{
>>> + unsigned long flags;
>>> +
>>> + /*
>>> + * loan/"inflate" the newpage first.
>>> + *
>>> + * We might race against the cmm_thread who might discover after our
>>> + * loan request that another page is to be unloaned. However, once
>>> + * the cmm_thread runs again later, this error will automatically
>>> + * be corrected.
>>> + */
>>> + if (plpar_page_set_loaned(newpage)) {
>>> + /* Unlikely, but possible. Tell the caller not to retry now. */
>>> + pr_err_ratelimited("%s: Cannot set page to loaned.", __func__);
>>> + return -EBUSY;
>>> + }
>>> +
>>> + /* balloon page list reference */
>>> + get_page(newpage);
>>> +
>>> + spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>>> + balloon_page_insert(b_dev_info, newpage);
>>> + balloon_page_delete(page);
>>
>> I think I am missing a b_dev_info->isolated_pages-- here.
>
> I don't know this code at all, but looking at other balloon drivers they
> do seem to do that in roughly the same spot.
>
> I'll add it, how can we test that it's correct?
It's certainly correct. We increment when we isolate
(balloon_page_isolate()) and decrement when we un-isolate.
Un-isolate happens when we putback a isolated page
(balloon_page_putback() - migration aborted) or when we successfully
migrate it (via balloon_page_migrate()).
The issue is that we cannot decrement in balloon_page_migrate(), as we
have to hold the b_dev_info->pages_lock. That's why we have to do it in
the registered callback under lock.
Please note that b_dev_info->isolated_pages is only needed for a sanity
check in balloon_page_dequeue(). That's why I didn't notice during
testing. I wonder if we should at some point rip out that sanity check ...
Thanks and cheers!
>
> cheers
>
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-11-12 11:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 14:29 [PATCH v1 00/12] powerpc/pseries: CMM: Implement balloon compaction and remove isolate notifier David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 01/12] powerpc/pseries: CMM: Implement release() function for sysfs device David Hildenbrand
2019-11-14 9:08 ` Michael Ellerman
2019-11-14 12:21 ` David Hildenbrand
2019-11-20 10:35 ` David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 02/12] powerpc/pseries: CMM: Report errors when registering notifiers fails David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 03/12] powerpc/pseries: CMM: Cleanup rc handling in cmm_init() David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 04/12] powerpc/pseries: CMM: Drop page array David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 05/12] powerpc/pseries: CMM: Use adjust_managed_page_count() insted of totalram_pages_* David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 06/12] powerpc/pseries: CMM: Rip out memory isolate notifier David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 07/12] powerpc/pseries: CMM: Convert loaned_pages to an atomic_long_t David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 08/12] powerpc/pseries: CMM: Implement balloon compaction David Hildenbrand
2019-10-31 14:35 ` David Hildenbrand
2019-11-12 10:46 ` Michael Ellerman
2019-11-12 11:12 ` David Hildenbrand [this message]
2019-11-13 11:08 ` Michael Ellerman
2019-10-31 14:29 ` [PATCH v1 09/12] powerpc/pseries: CMM: Switch to balloon_page_alloc() David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 10/12] powerpc/pseries: CMM: Simulation mode David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 11/12] mm: remove the memory isolate notifier David Hildenbrand
2019-10-31 14:29 ` [PATCH v1 12/12] mm: remove "count" parameter from has_unmovable_pages() David Hildenbrand
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