On 10/12/19 5:30 PM, Mina Almasry wrote:
A follow up patch in this series adds hugetlb cgroup uncharge info the file_region entries in resv->regions. The cgroup uncharge info may differ for different regions, so they can no longer be coalesced at region_add time. So, disable region coalescing in region_add in this patch.
Behavior change:
Say a resv_map exists like this [0->1], [2->3], and [5->6].
Then a region_chg/add call comes in region_chg/add(f=0, t=5).
Old code would generate resv->regions: [0->5], [5->6]. New code would generate resv->regions: [0->1], [1->2], [2->3], [3->5], [5->6].
Special care needs to be taken to handle the resv->adds_in_progress variable correctly. In the past, only 1 region would be added for every region_chg and region_add call. But now, each call may add multiple regions, so we can no longer increment adds_in_progress by 1 in region_chg, or decrement adds_in_progress by 1 after region_add or region_abort. Instead, region_chg calls add_reservation_in_range() to count the number of regions needed and allocates those, and that info is passed to region_add and region_abort to decrement adds_in_progress correctly.
Signed-off-by: Mina Almasry almasrymina@google.com
Changes in v6:
- Fix bug in number of region_caches allocated by region_chg
mm/hugetlb.c | 256 +++++++++++++++++++++++++++++---------------------- 1 file changed, 147 insertions(+), 109 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 4a60d7d44b4c3..f9c1947925bb9 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c
<snip>
-static long region_chg(struct resv_map *resv, long f, long t) +static long region_chg(struct resv_map *resv, long f, long t,
long *out_regions_needed)
{
struct file_region *trg = NULL; long chg = 0;
/* Allocate the maximum number of regions we're going to need for this
* reservation. The maximum number of regions we're going to need is
* (t - f) / 2 + 1, which corresponds to a region with alternating
* reserved and unreserved pages.
*/
*out_regions_needed = (t - f) / 2 + 1;
spin_lock(&resv->lock);
-retry_locked:
- resv->adds_in_progress++;
resv->adds_in_progress += *out_regions_needed;
/*
- Check for sufficient descriptors in the cache to accommodate
- the number of in progress add operations.
*/
- if (resv->adds_in_progress > resv->region_cache_count) {
struct file_region *trg;
VM_BUG_ON(resv->adds_in_progress - resv->region_cache_count > 1);
- while (resv->region_cache_count < resv->adds_in_progress) { /* Must drop lock to allocate a new descriptor. */
spin_unlock(&resv->lock);resv->adds_in_progress--;
- trg = kmalloc(sizeof(*trg), GFP_KERNEL); if (!trg) return -ENOMEM;
@@ -393,9 +395,9 @@ static long region_chg(struct resv_map *resv, long f, long t) spin_lock(&resv->lock); list_add(&trg->link, &resv->region_cache); resv->region_cache_count++;
}goto retry_locked;
I know that I suggested allocating the worst case number of entries, but this is going to be too much of a hit for existing hugetlbfs users. It is not uncommon for DBs to have a shared areas in excess of 1TB mapped by hugetlbfs. With this new scheme, the above while loop will allocate over a half million file region entries and end up only using one.
I think we need to step back and come up with a different approach. Let me give it some more thought before throwing out ideas that may waste more of your time. Sorry.