* [PATCH] mm/hugetlb: document the reserve map/region tracking routines
@ 2015-05-26 21:27 Mike Kravetz
2015-05-26 23:09 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Mike Kravetz @ 2015-05-26 21:27 UTC (permalink / raw)
To: linux-mm, linux-kernel
Cc: Naoya Horiguchi, Davidlohr Bueso, David Rientjes,
Luiz Capitulino, Andrew Morton, Mike Kravetz
This is a documentation only patch and does not modify any code.
Descriptions of the routines used for reserve map/region tracking
are added.
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 50 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 54f129d..ad2c628 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -212,8 +212,20 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
* Region tracking -- allows tracking of reservations and instantiated pages
* across the pages in a mapping.
*
- * The region data structures are embedded into a resv_map and
- * protected by a resv_map's lock
+ * The region data structures are embedded into a resv_map and protected
+ * by a resv_map's lock. The set of regions within the resv_map represent
+ * reservations for huge pages, or huge pages that have already been
+ * instantiated within the map. The from and to elements are huge page
+ * indicies into the associated mapping. from indicates the starting index
+ * of the region. to represents the first index past the end of the region.
+ *
+ * For example, a file region structure with from == 0 and to == 4 represents
+ * four huge pages in a mapping. It is important to note that the to element
+ * represents the first element past the end of the region. This is used in
+ * arithmetic as 4(to) - 0(from) = 4 huge pages in the region.
+ *
+ * Interval notation of the form [from, to) will be used to indicate that
+ * the endpoint from is inclusive and to is exclusive.
*/
struct file_region {
struct list_head link;
@@ -221,6 +233,14 @@ struct file_region {
long to;
};
+/*
+ * Add the huge page range represented by [f, t) to the reserve
+ * map. Existing regions will be expanded to accommodate the
+ * specified range. We know only existing regions need to be
+ * expanded, because region_add is only called after region_chg
+ * with the same range. If a new file_region structure must
+ * be allocated, it is done in region_chg.
+ */
static long region_add(struct resv_map *resv, long f, long t)
{
struct list_head *head = &resv->regions;
@@ -260,6 +280,25 @@ static long region_add(struct resv_map *resv, long f, long t)
return 0;
}
+/*
+ * Examine the existing reserve map and determine how many
+ * huge pages in the specified range [f, t) are NOT currently
+ * represented. This routine is called before a subsequent
+ * call to region_add that will actually modify the reserve
+ * map to add the specified range [f, t). region_chg does
+ * not change the number of huge pages represented by the
+ * map. However, if the existing regions in the map can not
+ * be expanded to represent the new range, a new file_region
+ * structure is added to the map as a placeholder. This is
+ * so that the subsequent region_add call will have all the
+ * regions it needs and will not fail.
+ *
+ * Returns the number of huge pages that need to be added
+ * to the existing reservation map for the range [f, t).
+ * This number is greater or equal to zero. -ENOMEM is
+ * returned if a new file_region structure is needed and can
+ * not be allocated.
+ */
static long region_chg(struct resv_map *resv, long f, long t)
{
struct list_head *head = &resv->regions;
@@ -326,6 +365,11 @@ out_nrg:
return chg;
}
+/*
+ * Truncate the reserve map at index 'end'. Modify/truncate any
+ * region which contains end. Delete any regions past end.
+ * Return the number of huge pages removed from the map.
+ */
static long region_truncate(struct resv_map *resv, long end)
{
struct list_head *head = &resv->regions;
@@ -361,6 +405,10 @@ out:
return chg;
}
+/*
+ * Count and return the number of huge pages in the reserve map
+ * that intersect with the range [f, t).
+ */
static long region_count(struct resv_map *resv, long f, long t)
{
struct list_head *head = &resv->regions;
--
2.1.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/hugetlb: document the reserve map/region tracking routines
2015-05-26 21:27 [PATCH] mm/hugetlb: document the reserve map/region tracking routines Mike Kravetz
@ 2015-05-26 23:09 ` Andrew Morton
2015-05-27 3:30 ` Mike Kravetz
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2015-05-26 23:09 UTC (permalink / raw)
To: Mike Kravetz
Cc: linux-mm, linux-kernel, Naoya Horiguchi, Davidlohr Bueso,
David Rientjes, Luiz Capitulino
On Tue, 26 May 2015 14:27:10 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:
> This is a documentation only patch and does not modify any code.
> Descriptions of the routines used for reserve map/region tracking
> are added.
Confused. This adds comments which are similar to the ones which were
added by
mm-hugetlb-compute-return-the-number-of-regions-added-by-region_add-v2.patch
and
mm-hugetlb-handle-races-in-alloc_huge_page-and-hugetlb_reserve_pages-v2.patch.
But the comments are a bit different. And this patch madly conflicts
with the two abovementioned patches.
Maybe the thing to do is to start again, with a three-patch series:
mm-hugetlb-document-the-reserve-map-region-tracking-routines.patch
mm-hugetlb-compute-return-the-number-of-regions-added-by-region_add-v3.patch
mm-hugetlb-handle-races-in-alloc_huge_page-and-hugetlb_reserve_pages-v3.patch
while resolving the differences in the new code comments?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/hugetlb: document the reserve map/region tracking routines
2015-05-26 23:09 ` Andrew Morton
@ 2015-05-27 3:30 ` Mike Kravetz
0 siblings, 0 replies; 3+ messages in thread
From: Mike Kravetz @ 2015-05-27 3:30 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, linux-kernel, Naoya Horiguchi, Davidlohr Bueso,
David Rientjes, Luiz Capitulino
On 05/26/2015 04:09 PM, Andrew Morton wrote:
> On Tue, 26 May 2015 14:27:10 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
>> This is a documentation only patch and does not modify any code.
>> Descriptions of the routines used for reserve map/region tracking
>> are added.
>
> Confused. This adds comments which are similar to the ones which were
> added by
> mm-hugetlb-compute-return-the-number-of-regions-added-by-region_add-v2.patch
> and
> mm-hugetlb-handle-races-in-alloc_huge_page-and-hugetlb_reserve_pages-v2.patch.
> But the comments are a bit different. And this patch madly conflicts
> with the two abovementioned patches.
>
> Maybe the thing to do is to start again, with a three-patch series:
>
> mm-hugetlb-document-the-reserve-map-region-tracking-routines.patch
> mm-hugetlb-compute-return-the-number-of-regions-added-by-region_add-v3.patch
> mm-hugetlb-handle-races-in-alloc_huge_page-and-hugetlb_reserve_pages-v3.patch
>
> while resolving the differences in the new code comments?
>
Sorry for the confusion. Naoya and Davidlohr suggested changes to
the documentation and code. One suggestion was to create a separate
documentation only patch.
I will create a new series as you suggest above.
--
Mike Kravetz
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-05-26 23:09 ` Andrew Morton
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