Messages in this thread |  | | Date | Wed, 22 Jul 2015 15:03:27 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH v4 01/10] mm/hugetlb: add cache of descriptors to resv_map for region_add |
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On Tue, 21 Jul 2015 11:09:35 -0700 Mike Kravetz <mike.kravetz@oracle.com> 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. > > ... > > --- 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; > };
Linux style is to spell words out fully: rgn->region. One advantage of doing this is that we get consistency: when there's no doubt about how a thing is spelled we don't end up with various different terms for the same thing. Note that we already have resv_map.regions and struct file_region.
To avoid a respin I think I'll just do a s/rgn/region/g on the patches then take a look for 80 col overflow - shout at me if you dislike that.
And yes, resv_map should have been called reservation_map. I suck.
And there's region_chg. Who wrote this stuff.
As an off-topic cleanup, resv_map and its associated stuff could be moved out of include/linux/hugetlb.h and made private to hugetlb.c with some minor changes.
Finally, the data structure definition site is a great place at which to document the overall design. What the fields do, how they interact, locking design, etc. eg, what data structure is at resv_map.region_cache, how is it managed, what purpose does it serve etc.
And adds_in_progress is interesting. I see the comment over region_abort() (rgn_abort?!) but haven't quite soaked that in yet.
> > ... > > @@ -312,11 +339,16 @@ static long region_add(struct resv_map *resv, long f, long t) > * so that the subsequent region_add call will have all the > * regions it needs and will not fail. > * > + * Upon entry, region_chg will also examine the cache of > + * region descriptors associated with the map. If there
"are"
> + * not enough descriptors cached, one will be allocated > + * for the in progress add operation. > + * > * 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. > + * returned if a new file_region structure or cache entry > + * is needed and can not be allocated. > */ > static long region_chg(struct resv_map *resv, long f, long t) > { > > ... >
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