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Re: [Qemu-devel] [Xen-devel] frequently ballooning results in qemu exit
From: |
Stefano Stabellini |
Subject: |
Re: [Qemu-devel] [Xen-devel] frequently ballooning results in qemu exit |
Date: |
Fri, 29 Mar 2013 12:37:29 +0000 |
User-agent: |
Alpine 2.02 (DEB 1266 2009-07-14) |
On Mon, 25 Mar 2013, Hanweidong wrote:
> We fixed this issue by below patch which computed the correct size for
> test_bits(). qemu_get_ram_ptr() and qemu_safe_ram_ptr() will call
> xen_map_cache() with size is 0 if the requested address is in the RAM. Then
> xen_map_cache() will pass the size 0 to test_bits() for checking if the
> corresponding pfn was mapped in cache. But test_bits() will always return 1
> when size is 0 without any bit testing. Actually, for this case, test_bits
> should check one bit. So this patch introduced a __test_bit_size which is
> greater than 0 and a multiple of XC_PAGE_SIZE, then test_bits can work
> correctly with __test_bit_size >> XC_PAGE_SHIFT as its size.
>
> Signed-off-by: Zhenguo Wang <address@hidden>
> Signed-off-by: Weidong Han <address@hidden>
Thanks for the patch and for debugging this difficult problem.
The reality is that size is never actually 0: when qemu_get_ram_ptr
calls xen_map_cache with size 0, it actually means "map until the end of
the page". As a consequence test_bits should always test at least 1 bit,
like you wrote.
I tried to simplify your patch a bit, does this one work for you?
diff --git a/xen-mapcache.c b/xen-mapcache.c
index dc6d1fa..b03b373 100644
--- a/xen-mapcache.c
+++ b/xen-mapcache.c
@@ -202,6 +202,7 @@ uint8_t *xen_map_cache(hwaddr phys_addr, hwaddr size,
hwaddr address_index;
hwaddr address_offset;
hwaddr __size = size;
+ hwaddr __test_bit_size = size >> XC_PAGE_SHIFT;
bool translated = false;
tryagain:
@@ -224,12 +225,16 @@ tryagain:
} else {
__size = MCACHE_BUCKET_SIZE;
}
+ /* always test at least one page */
+ if (!__test_bit_size) {
+ __test_bit_size = 1UL;
+ }
entry = &mapcache->entry[address_index % mapcache->nr_buckets];
while (entry && entry->lock && entry->vaddr_base &&
(entry->paddr_index != address_index || entry->size != __size ||
- !test_bits(address_offset >> XC_PAGE_SHIFT, size >> XC_PAGE_SHIFT,
+ !test_bits(address_offset >> XC_PAGE_SHIFT, __test_bit_size,
entry->valid_mapping))) {
pentry = entry;
entry = entry->next;
@@ -241,13 +246,13 @@ tryagain:
} else if (!entry->lock) {
if (!entry->vaddr_base || entry->paddr_index != address_index ||
entry->size != __size ||
- !test_bits(address_offset >> XC_PAGE_SHIFT, size >>
XC_PAGE_SHIFT,
+ !test_bits(address_offset >> XC_PAGE_SHIFT, __test_bit_size,
entry->valid_mapping)) {
xen_remap_bucket(entry, __size, address_index);
}
}
- if(!test_bits(address_offset >> XC_PAGE_SHIFT, size >> XC_PAGE_SHIFT,
+ if(!test_bits(address_offset >> XC_PAGE_SHIFT, __test_bit_size,
entry->valid_mapping)) {
mapcache->last_address_index = -1;
if (!translated && mapcache->phys_offset_to_gaddr) {