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Date: Mon, 26 Jan 2015 12:41:55 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC: "Kirill A. Shutemov" <kirill@...temov.name>,
David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] mm/thp: Allocate transparent hugepages on local node
On 01/21/2015 01:48 AM, Andrew Morton wrote:
> On Tue, 20 Jan 2015 17:04:31 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
>> + * Should be called with the mm_sem of the vma hold.
>
> That's a pretty cruddy sentence, isn't it? Copied from
> alloc_pages_vma(). "vma->vm_mm->mmap_sem" would be better.
>
> And it should tell us whether mmap_sem required a down_read or a
> down_write. What purpose is it serving?
This is already said for mmap_sem further above this comment line, which
should be just deleted (and from alloc_hugepage_vma comment too).
>> + *
>> + */
>> +struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
>> + unsigned long addr, int order)
>
> This pointlessly bloats the kernel if CONFIG_TRANSPARENT_HUGEPAGE=n?
>
>
>
> --- a/mm/mempolicy.c~mm-thp-allocate-transparent-hugepages-on-local-node-fix
> +++ a/mm/mempolicy.c
How about this cleanup on top? I'm not fully decided on the GFP_TRANSHUGE test.
This is potentially false positive, although I doubt anything else uses the same
gfp mask bits.
Should "hugepage" be extra bool parameter instead? Should I #ifdef the parameter
only for CONFIG_TRANSPARENT_HUGEPAGE, or is it not worth the ugliness?
--------8<--------
From: Vlastimil Babka <vbabka@...e.cz>
Date: Mon, 26 Jan 2015 11:41:33 +0100
Subject: [PATCH] mm/mempolicy: merge alloc_hugepage_vma to alloc_pages_vma
Commit "mm/thp: allocate transparent hugepages on local node" has introduced
alloc_hugepage_vma() to mm/mempolicy.c to perform a special policy for THP
allocations. The function has the same interface as alloc_pages_vma(), shares
a lot of boilerplate code and a long comment.
This patch merges the hugepage special case into alloc_pages_vma. The extra if
condition should be cheap enough price to pay. We also prevent a (however
unlikely) race with parallel mems_allowed update, which could make hugepage
allocation restart only within the fallback call to alloc_hugepage_vma() and
not reconsider the special rule in alloc_hugepage_vma().
Also by making sure mpol_cond_put(pol) is always called before actual
allocation attempt, we can use a single exit path within the function.
Also update the comment for missing node parameter and obsolete reference to
mm_sem.
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
include/linux/gfp.h | 4 +-
mm/mempolicy.c | 121 ++++++++++++++++------------------------------------
2 files changed, 39 insertions(+), 86 deletions(-)
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 60110e0..c19318d 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -335,8 +335,8 @@ alloc_pages(gfp_t gfp_mask, unsigned int order)
extern struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
struct vm_area_struct *vma, unsigned long addr,
int node);
-extern struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
- unsigned long addr, int order);
+#define alloc_hugepage_vma(gfp_mask, vma, addr, order) \
+ alloc_pages_vma(gfp_mask, order, vma, addr, numa_node_id())
#else
#define alloc_pages(gfp_mask, order) \
alloc_pages_node(numa_node_id(), gfp_mask, order)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 67b2d39..fd132c9 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1988,15 +1988,14 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
* @order:Order of the GFP allocation.
* @vma: Pointer to VMA or NULL if not available.
* @addr: Virtual Address of the allocation. Must be inside the VMA.
+ * @node: Which node to prefer for allocation (modulo policy).
*
* This function allocates a page from the kernel page pool and applies
* a NUMA policy associated with the VMA or the current process.
* When VMA is not NULL caller must hold down_read on the mmap_sem of the
* mm_struct of the VMA to prevent it from going away. Should be used for
- * all allocations for pages that will be mapped into
- * user space. Returns NULL when no page can be allocated.
- *
- * Should be called with the mm_sem of the vma hold.
+ * all allocations for pages that will be mapped into user space. Returns
+ * NULL when no page can be allocated.
*/
struct page *
alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
@@ -2005,103 +2004,57 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
struct mempolicy *pol;
struct page *page;
unsigned int cpuset_mems_cookie;
+ struct zonelist *zl;
+ nodemask_t *nmask;
retry_cpuset:
pol = get_vma_policy(vma, addr);
cpuset_mems_cookie = read_mems_allowed_begin();
- if (unlikely(pol->mode == MPOL_INTERLEAVE)) {
+ /*
+ * Detect hugepage allocations from the gfp mask. Ignore __GFP_WAIT
+ * which may be removed from gfp by alloc_hugepage_gfpmask()
+ */
+ if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+ ((gfp & (GFP_TRANSHUGE & ~__GFP_WAIT))
+ == (GFP_TRANSHUGE & ~__GFP_WAIT)) &&
+ pol->mode != MPOL_INTERLEAVE) {
+ /*
+ * For hugepage allocation and non-interleave policy which
+ * allows the current node, we only try to allocate from the
+ * current node and don't fall back to other nodes, as the
+ * cost of remote accesses would likely offset THP benefits.
+ *
+ * If the policy is interleave, or does not allow the current
+ * node in its nodemask, we allocate the standard way.
+ */
+ nmask = policy_nodemask(gfp, pol);
+ if (!nmask || node_isset(node, *nmask)) {
+ mpol_cond_put(pol);
+ page = alloc_pages_exact_node(node, gfp, order);
+ goto out;
+ }
+ }
+
+ if (pol->mode == MPOL_INTERLEAVE) {
unsigned nid;
nid = interleave_nid(pol, vma, addr, PAGE_SHIFT + order);
mpol_cond_put(pol);
page = alloc_page_interleave(gfp, order, nid);
- if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
- goto retry_cpuset;
-
- return page;
+ goto out;
}
- page = __alloc_pages_nodemask(gfp, order,
- policy_zonelist(gfp, pol, node),
- policy_nodemask(gfp, pol));
+
+ nmask = policy_nodemask(gfp, pol);
+ zl = policy_zonelist(gfp, pol, node);
mpol_cond_put(pol);
+ page = __alloc_pages_nodemask(gfp, order, zl, nmask);
+out:
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
}
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-/**
- * alloc_hugepage_vma: Allocate a hugepage for a VMA
- * @gfp:
- * %GFP_USER user allocation.
- * %GFP_KERNEL kernel allocations,
- * %GFP_HIGHMEM highmem/user allocations,
- * %GFP_FS allocation should not call back into a file system.
- * %GFP_ATOMIC don't sleep.
- *
- * @vma: Pointer to VMA or NULL if not available.
- * @addr: Virtual Address of the allocation. Must be inside the VMA.
- * @order: Order of the hugepage for gfp allocation.
- *
- * This functions allocate a huge page from the kernel page pool and applies
- * a NUMA policy associated with the VMA or the current process.
- * For policy other than %MPOL_INTERLEAVE, we make sure we allocate hugepage
- * only from the current node if the current node is part of the node mask.
- * If we can't allocate a hugepage we fail the allocation and don' try to fallback
- * to other nodes in the node mask. If the current node is not part of node mask
- * or if the NUMA policy is MPOL_INTERLEAVE we use the allocator that can
- * fallback to nodes in the policy node mask.
- *
- * When VMA is not NULL caller must hold down_read on the mmap_sem of the
- * mm_struct of the VMA to prevent it from going away. Should be used for
- * all allocations for pages that will be mapped into
- * user space. Returns NULL when no page can be allocated.
- *
- * Should be called with vma->vm_mm->mmap_sem held.
- *
- */
-struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
- unsigned long addr, int order)
-{
- struct page *page;
- nodemask_t *nmask;
- struct mempolicy *pol;
- int node = numa_node_id();
- unsigned int cpuset_mems_cookie;
-
-retry_cpuset:
- pol = get_vma_policy(vma, addr);
- cpuset_mems_cookie = read_mems_allowed_begin();
- /*
- * For interleave policy, we don't worry about
- * current node. Otherwise if current node is
- * in nodemask, try to allocate hugepage from
- * the current node. Don't fall back to other nodes
- * for THP.
- */
- if (unlikely(pol->mode == MPOL_INTERLEAVE))
- goto alloc_with_fallback;
- nmask = policy_nodemask(gfp, pol);
- if (!nmask || node_isset(node, *nmask)) {
- mpol_cond_put(pol);
- page = alloc_pages_exact_node(node, gfp, order);
- if (unlikely(!page &&
- read_mems_allowed_retry(cpuset_mems_cookie)))
- goto retry_cpuset;
- return page;
- }
-alloc_with_fallback:
- mpol_cond_put(pol);
- /*
- * if current node is not part of node mask, try
- * the allocation from any node, and we can do retry
- * in that case.
- */
- return alloc_pages_vma(gfp, order, vma, addr, node);
-}
-#endif
-
/**
* alloc_pages_current - Allocate pages.
*
--
2.1.2
--
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