Re: [PATCH v8, part3 10/14] mm: use a dedicated lock to protect totalram_pagesand zone->managed_pages

From: Jiang Liu
Date: Tue Jun 11 2013 - 22:18:28 EST

On Wed 12 Jun 2013 04:00:42 AM CST, Andrew Morton wrote:
> On Sun, 26 May 2013 21:38:38 +0800 Jiang Liu <liuj97@xxxxxxxxx> wrote:
>> Currently lock_memory_hotplug()/unlock_memory_hotplug() are used to
>> protect totalram_pages and zone->managed_pages. Other than the memory
>> hotplug driver, totalram_pages and zone->managed_pages may also be
>> modified at runtime by other drivers, such as Xen balloon,
>> virtio_balloon etc. For those cases, memory hotplug lock is a little
>> too heavy, so introduce a dedicated lock to protect totalram_pages
>> and zone->managed_pages.
>> Now we have a simplified locking rules totalram_pages and
>> zone->managed_pages as:
>> 1) no locking for read accesses because they are unsigned long.
>> 2) no locking for write accesses at boot time in single-threaded context.
>> 3) serialize write accesses at runtime by acquiring the dedicated
>> managed_page_count_lock.
>> Also adjust zone->managed_pages when freeing reserved pages into the
>> buddy system, to keep totalram_pages and zone->managed_pages in
>> consistence.
>> ...
>> +void adjust_managed_page_count(struct page *page, long count)
>> +{
>> + spin_lock(&managed_page_count_lock);
>> + page_zone(page)->managed_pages += count;
>> + totalram_pages += count;
>> + spin_unlock(&managed_page_count_lock);
>> +}
>> +EXPORT_SYMBOL(adjust_managed_page_count);
> This is exported to modules but there are no modular callers at this
> time.
> I assume this was done for some forthcoming xen/virtio_balloon/etc
> patches? If so, it would be better to avoid adding the export until it
> is actually needed.
Hi Andrew,
adjust_managed_page_count() will be used by virtio_balloon and xen
drivers. Grep mmots tree:
drivers/virtio/virtio_balloon.c: adjust_managed_page_count(page, -1);
drivers/virtio/virtio_balloon.c: adjust_managed_page_count(page, 1);
drivers/xen/balloon.c: adjust_managed_page_count(page, -1);
drivers/xen/balloon.c: adjust_managed_page_count(page, 1);

So if we un-export it in part3, we need to export in part4 again.

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