On 07/17/2015 02:02 AM, Naoya Horiguchi wrote:
> On Sun, Jul 12, 2015 at 09:20:59PM -0700, Mike Kravetz wrote:
>> fallocate hole punch will want to remove a specific range of
>> pages. When pages are removed, their associated entries in
>> the region/reserve map will also be removed. This will break
>> an assumption in the region_chg/region_add calling sequence.
>> If a new region descriptor must be allocated, it is done as
>> part of the region_chg processing. In this way, region_add
>> can not fail because it does not need to attempt an allocation.
>>
>> To prepare for fallocate hole punch, create a "cache" of
>> descriptors that can be used by region_add if necessary.
>> region_chg will ensure there are sufficient entries in the
>> cache. It will be necessary to track the number of in progress
>> add operations to know a sufficient number of descriptors
>> reside in the cache. A new routine region_abort is added to
>> adjust this in progress count when add operations are aborted.
>> vma_abort_reservation is also added for callers creating
>> reservations with vma_needs_reservation/vma_commit_reservation.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> ---
>> include/linux/hugetlb.h | 3 +
>> mm/hugetlb.c | 169 ++++++++++++++++++++++++++++++++++++++++++------
>> 2 files changed, 153 insertions(+), 19 deletions(-)
>>
>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>> index d891f94..667cf44 100644
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -35,6 +35,9 @@ struct resv_map {
>> struct kref refs;
>> spinlock_t lock;
>> struct list_head regions;
>> + long adds_in_progress;
>> + struct list_head rgn_cache;
>> + long rgn_cache_count;
>> };
>> extern struct resv_map *resv_map_alloc(void);
>> void resv_map_release(struct kref *ref);
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index a8c3087..241d16d 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -240,11 +240,14 @@ struct file_region {
>>
>> /*
>> * 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.
>> + * map. In the normal case, existing regions will be expanded
>> + * to accommodate the specified range. Sufficient regions should
>> + * exist for expansion due to the previous call to region_chg
>> + * with the same range. However, it is possible that region_del
>> + * could have been called after region_chg and modifed the map
>> + * in such a way that no region exists to be expanded. In this
>> + * case, pull a region descriptor from the cache associated with
>> + * the map and use that for the new range.
>> *
>> * Return the number of new huge pages added to the map. This
>> * number is greater than or equal to zero.
>> @@ -261,6 +264,27 @@ static long region_add(struct resv_map *resv, long f, long t)
>> if (f <= rg->to)
>> break;
>>
>> + if (&rg->link == head || t < rg->from) {
>> + /*
>> + * No region exists which can be expanded to include the
>> + * specified range. Pull a region descriptor from the
>> + * cache, and use it for this range.
>> + */
>
> This comment mentions this if-block, not the VM_BUG_ON below, so it had
> better be put the above if-line.
OK, I will move and make a minor modification to the comment.
>
>> + VM_BUG_ON(!resv->rgn_cache_count);
>
> resv->rgn_cache_count <= 0 might be safer.
Sure.
> ...
>> @@ -3236,11 +3360,14 @@ retry:
>> * any allocations necessary to record that reservation occur outside
>> * the spinlock.
>> */
>> - if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
>> + if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
>> if (vma_needs_reservation(h, vma, address) < 0) {
>> ret = VM_FAULT_OOM;
>> goto backout_unlocked;
>> }
>> + /* Just decrements count, does not deallocate */
>> + vma_abort_reservation(h, vma, address);
>> + }
>
> This is not "abort reservation" operation, but you use "abort reservation"
> routine, which might confusing and makes future maintenance hard. I think
> this should be done in a simplified variant of vma_commit_reservation()
> (maybe just an alias of your vma_abort_reservation()) or fast path in
> vma_commit_reservation().
I am struggling a bit with the names of these routines. The
routines in question are:
vma_needs_reservation - This is a wrapper for region_chg(), so the
return value is the number of regions needed for the page.
Since there is only one page, the routine effectively
becomes a boolean. Hence the name "needs".
vma_commit_reservation - This is a wrapper for region_add(). It
must be called after a prior call to vma_needs_reservation
and after actual allocation of the page.
We need a way to handle the case where vma_needs_reservation has
been called, but the page allocation is not successful. I chose
the name vma_abort_reservation, but as noted (even in my comments)
it is not an actual abort.
I am not sure if you are suggesting vma_commit_reservation() should
handle this as a special case. I think a separately named routine which
indicates and end of the reservation/allocation process would be
easier to understand.
What about changing the name vma_abort_reservation() to
vma_end_reservation()? This would indicate that the reservation/
allocation process is ended.
> Thanks,
> Naoya Horiguchi
Thank you for your reviews.
--
Mike Kravetz
>
>>
>> ptl = huge_pte_lockptr(h, mm, ptep);
>> spin_lock(ptl);
>> @@ -3387,6 +3514,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>> ret = VM_FAULT_OOM;
>> goto out_mutex;
>> }
>> + /* Just decrements count, does not deallocate */
>> + vma_abort_reservation(h, vma, address);
>>
>> if (!(vma->vm_flags & VM_MAYSHARE))
>> pagecache_page = hugetlbfs_pagecache_page(h,
>> @@ -3726,6 +3855,8 @@ int hugetlb_reserve_pages(struct inode *inode,
>> }
>> return 0;
>> out_err:
>> + if (!vma || vma->vm_flags & VM_MAYSHARE)
>> + region_abort(resv_map, from, to);
>> if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
>> kref_put(&resv_map->refs, resv_map_release);
>> return ret;
>> --
>> 2.1.0
--
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