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SubjectRe: [PATCH 5 of 5] xen: Avoid allocations causing swap activity on the resume path
Jeff Garzik wrote:
> Jeremy Fitzhardinge wrote:
>> From: Ian Campbell <ian.campbell@citrix.com>
>>
>> Avoid allocations causing swap activity on the resume path by allowing
>> such allocations to access the emergency pools otherwise a
>> save/restore/migration of a guest which is low on memory can
>> deadlock.
>>
>> [ linux-2.6.18-xen changesets e8b49cfbdac, fdb998e79aba ]
>>
>> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>> ---
>> drivers/block/xen-blkfront.c | 5 +++--
>> drivers/net/xen-netfront.c | 4 ++--
>> drivers/xen/xenbus/xenbus_client.c | 2 +-
>> drivers/xen/xenbus/xenbus_xs.c | 10 +++++-----
>> 4 files changed, 11 insertions(+), 10 deletions(-)
>
> IMO I am not qualified enough to ACK or NAK this VM-related patch...

Yeah, I'm not quite sure about which GFP_ flags to use in what
circumstance. In this case the potential for deadlock exists because
this is the code which is reconnecting the virtual devices after a
resume, which will probably include its storage (either block device, or
some kind of network storage). Should GFP_NOFS also be in there?
Something else? Does __GFP_HIGH necessarily mean that it won't try to
do IO to push pages out?

Thanks,
J


Patch again for reference:

Subject: xen: Avoid allocations causing swap activity on the resume path

From: Ian Campbell <ian.campbell@citrix.com>

Avoid allocations causing swap activity on the resume path by allowing
such allocations to access the emergency pools otherwise a
save/restore/migration of a guest which is low on memory can
deadlock.

[ linux-2.6.18-xen changesets e8b49cfbdac, fdb998e79aba ]

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

---
drivers/block/xen-blkfront.c | 5 +++--
drivers/net/xen-netfront.c | 4 ++--
drivers/xen/xenbus/xenbus_client.c | 2 +-
drivers/xen/xenbus/xenbus_xs.c | 10 +++++-----
4 files changed, 11 insertions(+), 10 deletions(-)

===================================================================
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -584,7 +584,7 @@

info->ring_ref = GRANT_INVALID_REF;

- sring = (struct blkif_sring *)__get_free_page(GFP_KERNEL);
+ sring = (struct blkif_sring *)__get_free_page(GFP_KERNEL | __GFP_HIGH);
if (!sring) {
xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
return -ENOMEM;
@@ -741,7 +741,8 @@
int j;

/* Stage 1: Make a safe copy of the shadow state. */
- copy = kmalloc(sizeof(info->shadow), GFP_KERNEL);
+ copy = kmalloc(sizeof(info->shadow),
+ GFP_KERNEL | __GFP_NOFAIL | __GFP_HIGH);
if (!copy)
return -ENOMEM;
memcpy(copy, info->shadow, sizeof(info->shadow));
===================================================================
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1324,7 +1324,7 @@
goto fail;
}

- txs = (struct xen_netif_tx_sring *)get_zeroed_page(GFP_KERNEL);
+ txs = (struct xen_netif_tx_sring *)get_zeroed_page(GFP_KERNEL | __GFP_HIGH);
if (!txs) {
err = -ENOMEM;
xenbus_dev_fatal(dev, err, "allocating tx ring page");
@@ -1340,7 +1340,7 @@
}

info->tx_ring_ref = err;
- rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_KERNEL);
+ rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_KERNEL | __GFP_HIGH);
if (!rxs) {
err = -ENOMEM;
xenbus_dev_fatal(dev, err, "allocating rx ring page");
===================================================================
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -117,7 +117,7 @@
char *path;

va_start(ap, pathfmt);
- path = kvasprintf(GFP_KERNEL, pathfmt, ap);
+ path = kvasprintf(GFP_KERNEL | __GFP_HIGH, pathfmt, ap);
va_end(ap);

if (!path) {
===================================================================
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -283,9 +283,9 @@
char *buffer;

if (strlen(name) == 0)
- buffer = kasprintf(GFP_KERNEL, "%s", dir);
+ buffer = kasprintf(GFP_KERNEL | __GFP_HIGH, "%s", dir);
else
- buffer = kasprintf(GFP_KERNEL, "%s/%s", dir, name);
+ buffer = kasprintf(GFP_KERNEL | __GFP_HIGH, "%s/%s", dir, name);
return (!buffer) ? ERR_PTR(-ENOMEM) : buffer;
}

@@ -297,7 +297,7 @@
*num = count_strings(strings, len);

/* Transfer to one big alloc for easy freeing. */
- ret = kmalloc(*num * sizeof(char *) + len, GFP_KERNEL);
+ ret = kmalloc(*num * sizeof(char *) + len, GFP_KERNEL | __GFP_HIGH);
if (!ret) {
kfree(strings);
return ERR_PTR(-ENOMEM);
@@ -751,7 +751,7 @@
}


- msg = kmalloc(sizeof(*msg), GFP_KERNEL);
+ msg = kmalloc(sizeof(*msg), GFP_KERNEL | __GFP_HIGH);
if (msg == NULL) {
err = -ENOMEM;
goto out;
@@ -763,7 +763,7 @@
goto out;
}

- body = kmalloc(msg->hdr.len + 1, GFP_KERNEL);
+ body = kmalloc(msg->hdr.len + 1, GFP_KERNEL | __GFP_HIGH);
if (body == NULL) {
kfree(msg);
err = -ENOMEM;




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