lkml.org 
[lkml]   [2012]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] x86: Avoid contention on cpa_lock if possible
Date
From: Shai Fultheim <shai@scalemp.com>

Some architectures (e.g. vSMP) do not require to serialize cpa, for
instance, by guaranteeing that the most recent TLB entry will always be
used.

To avoid needless contention on cpa_lock, do not lock/unlock it on such
architectures.

Signed-off-by: Shai Fultheim <shai@scalemp.com>
[ido@wizery.com: added should_serialize_cpa, handled potential race, and
reworded the commit message]
Signed-off-by: Ido Yariv <ido@wizery.com>
---
arch/x86/mm/pageattr.c | 36 ++++++++++++++++++++++++++++--------
1 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index e1ebde3..4d606ee 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -501,7 +501,7 @@ out_unlock:
return do_split;
}

-static int split_large_page(pte_t *kpte, unsigned long address)
+static int split_large_page(pte_t *kpte, unsigned long address, bool cpa_locked)
{
unsigned long pfn, pfninc = 1;
unsigned int i, level;
@@ -509,10 +509,10 @@ static int split_large_page(pte_t *kpte, unsigned long address)
pgprot_t ref_prot;
struct page *base;

- if (!debug_pagealloc)
+ if (cpa_locked)
spin_unlock(&cpa_lock);
base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
- if (!debug_pagealloc)
+ if (cpa_locked)
spin_lock(&cpa_lock);
if (!base)
return -ENOMEM;
@@ -624,7 +624,8 @@ static int __cpa_process_fault(struct cpa_data *cpa, unsigned long vaddr,
}
}

-static int __change_page_attr(struct cpa_data *cpa, int primary)
+static int __change_page_attr(struct cpa_data *cpa, int primary,
+ bool cpa_locked)
{
unsigned long address;
int do_split, err;
@@ -693,7 +694,7 @@ repeat:
/*
* We have to split the large page:
*/
- err = split_large_page(kpte, address);
+ err = split_large_page(kpte, address, cpa_locked);
if (!err) {
/*
* Do a global flush tlb after splitting the large page
@@ -787,9 +788,20 @@ static int cpa_process_alias(struct cpa_data *cpa)
return 0;
}

+static inline bool should_serialize_cpa(void)
+{
+ /*
+ * Some architectures do not require cpa() to be serialized, for
+ * instance, by guaranteeing that the most recent TLB entry will be
+ * used.
+ */
+ return !debug_pagealloc && !is_vsmp_box();
+}
+
static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
{
int ret, numpages = cpa->numpages;
+ bool cpa_locked = false;

while (numpages) {
/*
@@ -801,10 +813,18 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY))
cpa->numpages = 1;

- if (!debug_pagealloc)
+ if (should_serialize_cpa()) {
spin_lock(&cpa_lock);
- ret = __change_page_attr(cpa, checkalias);
- if (!debug_pagealloc)
+ /*
+ * In order to avoid any race conditions in which
+ * should_serialize_cpa() returns a different value
+ * after the lock was acquired, make sure locking is
+ * consitent and don't ever leave the lock acquired.
+ */
+ cpa_locked = true;
+ }
+ ret = __change_page_attr(cpa, checkalias, cpa_locked);
+ if (cpa_locked)
spin_unlock(&cpa_lock);
if (ret)
return ret;
--
1.7.7.6


\
 
 \ /
  Last update: 2012-04-06 14:43    [W:0.066 / U:0.656 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site