fallocate hole punch will want to remove a specific range of pages.
The existing region_truncate() routine deletes all region/reserve
map entries after a specified offset. region_del() will provide
this same functionality if the end of region is specified as -1.
Hence, region_del() can replace region_truncate().
Unlike region_truncate(), region_del() can return an error in the
rare case where it can not allocate memory for a region descriptor.
This ONLY happens in the case where an existing region must be split.
Current callers passing -1 as end of range will never experience
this error and do not need to deal with error handling. Future
callers of region_del() (such as fallocate hole punch) will need to
handle this error. A routine hugetlb_fix_reserve_counts() is added
to assist in cleaning up if fallocate hole punch experiences this
type of error in region_del().
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
include/linux/hugetlb.h | 1 +
mm/hugetlb.c | 99 ++++++++++++++++++++++++++++++++++++++-----------
2 files changed, 79 insertions(+), 21 deletions(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 7b57850..fd337f2 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -81,6 +81,7 @@ bool isolate_huge_page(struct page *page, struct list_head *list);
void putback_active_hugepage(struct page *page);
bool is_hugepage_active(struct page *page);
void free_huge_page(struct page *page);
+void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve);
#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 63f6d43..620cc9e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -261,38 +261,74 @@ out_nrg:
return chg;
}
-static long region_truncate(struct resv_map *resv, long end)
+static long region_del(struct resv_map *resv, long f, long t)
{
struct list_head *head = &resv->regions;
struct file_region *rg, *trg;
+ struct file_region *nrg = NULL;
long chg = 0;
+ /*
+ * Locate segments we overlap and etiher split, remove or
+ * trim the existing regions. The end of region (t) == -1
+ * indicates all remaining regions. Special case t == -1 as
+ * all comparisons are signed. Also, when t == -1 it is not
+ * possible to return an error (-ENOMEM) as this only happens
+ * when splitting a region. Callers take advantage of this
+ * when calling with -1.
+ */
+ if (t == -1)
+ t = LONG_MAX;
+retry:
spin_lock(&resv->lock);
- /* Locate the region we are either in or before. */
- list_for_each_entry(rg, head, link)
- if (end <= rg->to)
+ list_for_each_entry_safe(rg, trg, head, link) {
+ if (rg->to <= f)
+ continue;
+ if (rg->from >= t)
break;
- if (&rg->link == head)
- goto out;
- /* If we are in the middle of a region then adjust it. */
- if (end > rg->from) {
- chg = rg->to - end;
- rg->to = end;
- rg = list_entry(rg->link.next, typeof(*rg), link);
- }
+ if (f > rg->from && t < rg->to) { /* must split region */
+ if (!nrg) {
+ spin_unlock(&resv->lock);
+ nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
+ if (!nrg)
+ return -ENOMEM;
+ goto retry;
+ }
- /* Drop any remaining regions. */
- list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
- if (&rg->link == head)
+ chg += t - f;
+
+ /* new entry for end of split region */
+ nrg->from = t;
+ nrg->to = rg->to;
+ INIT_LIST_HEAD(&nrg->link);
+
+ /* original entry is trimmed */
+ rg->to = f;
+
+ list_add(&nrg->link, &rg->link);
+ nrg = NULL;
break;
- chg += rg->to - rg->from;
- list_del(&rg->link);
- kfree(rg);
+ }
+
+ if (f <= rg->from && t >= rg->to) { /* remove entire region */
+ chg += rg->to - rg->from;
+ list_del(&rg->link);
+ kfree(rg);
+ continue;
+ }
+
+ if (f <= rg->from) { /* trim beginning of region */
+ chg += t - rg->from;
+ rg->from = t;
+ } else { /* trim end of region */
+ chg += rg->to - f;
+ rg->to = f;
+ }
}
-out:
spin_unlock(&resv->lock);
+ kfree(nrg);
return chg;
}
@@ -324,6 +360,27 @@ static long region_count(struct resv_map *resv, long f, long t)
}
/*
+ * A rare out of memory error was encountered which prevented removal of
+ * the reserve map region for a page. The huge page itself was free''ed
+ * and removed from the page cache. This routine will adjust the global
+ * reserve count if needed, and the subpool usage count. By incrementing
+ * these counts, the reserve map entry which could not be deleted will
+ * appear as a "reserved" entry instead of simply dangling with incorrect
+ * counts.
+ */
+void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve)
+{
+ struct hugepage_subpool *spool = subpool_inode(inode);
+
+ if (restore_reserve) {
+ struct hstate *h = hstate_inode(inode);
+
+ h->resv_huge_pages++;
+ }
+ hugepage_subpool_get_pages(spool, 1);
+}
+
+/*
* Convert the address within this vma to the page offset within
* the mapping, in pagecache page units; huge pages here.
*/
@@ -427,7 +484,7 @@ void resv_map_release(struct kref *ref)
struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
/* Clear out any active regions before we release the map. */
- region_truncate(resv_map, 0);
+ region_del(resv_map, 0, -1);
kfree(resv_map);
}
@@ -3558,7 +3615,7 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
struct hugepage_subpool *spool = subpool_inode(inode);
if (resv_map)
- chg = region_truncate(resv_map, offset);
+ chg = region_del(resv_map, offset, -1);
spin_lock(&inode->i_lock);
inode->i_blocks -= (blocks_per_huge_page(h) * freed);
spin_unlock(&inode->i_lock);
--
2.1.0
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>