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From: Olaf Hering <olaf@aepfle.de>
To: Wei Liu <wei.liu2@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org
Subject: Re: [PATCH v3 3/3] tools/libxc: use superpages during restore of HVM guest
Date: Fri, 25 Aug 2017 16:51:51 +0200	[thread overview]
Message-ID: <20170825145151.GP6372@aepfle.de> (raw)
In-Reply-To: <20170825140015.GO6372@aepfle.de>


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On Fri, Aug 25, Olaf Hering wrote:

> I think with the new check of max_pages an overallocation can not happen
> anymore. If at some point the domU still has room for a superpage, it
> will be allocated. In case the batch does not fully fill the superpage,
> the holes will be freed. In the next batch no superpage can be allocated
> anymore, but single pages will be used.

There is one case where Over-allocation will happen: assume
x86_hvm_populate_pfns gets a batch of pfns that fit trigger the
allocation of a 1G page. All pfns will fit into that partly populated
superpage. Then the guest has a hole right after the max_pfn of that
batch. The next batch will start in a new superpage. As a result the
freeing part of x86_hvm_populate_pfns will not consider the previous
superpage anymore. Now 512MB are allocated, but unpopulated.

To handle this case the min_pfn/max_pfn have to be global so that the
current batch can free allocated pfns from previous batches.

Olaf

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      reply	other threads:[~2017-08-25 14:51 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-24 10:14 [PATCH v3 0/3] tools/libxc: use superpages Olaf Hering
2017-08-24 10:14 ` [PATCH v3 1/3] tools/libxc: move SUPERPAGE macros to common header Olaf Hering
2017-08-25 12:06   ` Wei Liu
2017-08-24 10:14 ` [PATCH v3 2/3] tools/libxc: add API for bitmap access for restore Olaf Hering
2017-08-25 12:06   ` Wei Liu
2017-08-24 10:14 ` [PATCH v3 3/3] tools/libxc: use superpages during restore of HVM guest Olaf Hering
2017-08-25 12:06   ` Wei Liu
2017-08-25 12:51     ` Olaf Hering
2017-08-25 13:36       ` Wei Liu
2017-08-25 14:00         ` Olaf Hering
2017-08-25 14:51           ` Olaf Hering [this message]

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