From: Michael Ellerman <mpe@ellerman•id.au>
To: David Hildenbrand <david@redhat•com>, linux-kernel@vger•kernel.org
Cc: "Enrico Weigelt, metux IT consult" <info@metux•net>,
Oliver O'Halloran <oohall@gmail•com>,
Pavel Tatashin <pasha.tatashin@soleen•com>,
Alexey Kardashevskiy <aik@ozlabs•ru>,
Gao Xiang <xiang@kernel•org>,
Greg Hackmann <ghackmann@google•com>,
David Howells <dhowells@redhat•com>,
linux-mm@kvack•org, Arun KS <arunks@codeaurora•org>,
Paul Mackerras <paulus@samba•org>,
Allison Randal <allison@lohutok•net>,
Christian Brauner <christian@brauner•io>,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Geert Uytterhoeven <geert@linux-m68k•org>,
Andrew Morton <akpm@linux-foundation•org>,
Todd Kjos <tkjos@google•com>,
linuxppc-dev@lists•ozlabs.org,
Thomas Gleixner <tglx@linutronix•de>,
Thiago Jung Bauermann <bauerman@linux•ibm.com>,
Anshuman Khandual <khandual@linux•vnet.ibm.com>
Subject: Re: [PATCH v1 08/12] powerpc/pseries: CMM: Implement balloon compaction
Date: Wed, 13 Nov 2019 22:08:44 +1100 [thread overview]
Message-ID: <87lfsk11ab.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <8e46b1c5-f52b-0155-4d4f-e3bbdea95384@redhat.com>
David Hildenbrand <david@redhat•com> writes:
> 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.
OK, I get it now.
> 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 ...
OK. Sanity checks can be good, though checks that call BUG() are less
nice :) But I'm not an mm expert so I'll defer to you folks on the
sanity check.
For now I've merged this series with the decrement added to
cmm_migratepage().
cheers
next prev parent reply other threads:[~2019-11-13 11:13 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
2019-11-13 11:08 ` Michael Ellerman [this message]
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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