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Michael S. TsirkinandAndrew Morton
47c81dadb7
At the moment, if a virtio balloon device has a page reporting vq but its
size is < PAGE_REPORTING_CAPACITY (32), the balloon driver fails probe.
But, there's no way for host to know this value, so it can easily create a
smaller vq and suddenly adding the reporting capability to the device
makes all of the driver fail. Not pretty.
Add a capacity field to page_reporting_dev_info so drivers can control the
maximum number of pages per report batch.
In virtio-balloon, set the capacity to the reporting virtqueue size,
letting page_reporting adapt to whatever the device provides.
Capacity need not be a power of two. Code previously called out division
by PAGE_REPORTING_CAPACITY as cheap since it was a power of 2, but no
performance difference was observed with non-power-of-2 values.
If capacity is 0 or exceeds PAGE_REPORTING_CAPACITY, it defaults to
PAGE_REPORTING_CAPACITY. The 0 check and the clamping is done in
page_reporting_register(), before the reporting work is scheduled, so we
never get division by 0.
Link: https://lore.kernel.org/444c24cf39f3f3620fc90ef4695bd6b0979f4c4b.1783232420.git.mst@redhat.com
Fixes: b0c504f154 ("virtio-balloon: add support for providing free page reports to host")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
33 lines
966 B
C
33 lines
966 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_PAGE_REPORTING_H
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#define _LINUX_PAGE_REPORTING_H
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#include <linux/mmzone.h>
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#include <linux/scatterlist.h>
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#define PAGE_REPORTING_CAPACITY 32
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#define PAGE_REPORTING_ORDER_UNSPECIFIED -1
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struct page_reporting_dev_info {
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/* function that alters pages to make them "reported" */
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int (*report)(struct page_reporting_dev_info *prdev,
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struct scatterlist *sg, unsigned int nents);
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/* work struct for processing reports */
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struct delayed_work work;
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/* Current state of page reporting */
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atomic_t state;
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/* Minimal order of page reporting */
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unsigned int order;
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/* Max pages per report batch; 0 (default) means PAGE_REPORTING_CAPACITY */
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unsigned int capacity;
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};
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/* Tear-down and bring-up for page reporting devices */
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void page_reporting_unregister(struct page_reporting_dev_info *prdev);
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int page_reporting_register(struct page_reporting_dev_info *prdev);
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#endif /*_LINUX_PAGE_REPORTING_H */
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