On Sat, Jun 09, 2012 at 06:39:06PM +0530, Aneesh Kumar K.V wrote: > Johannes Weiner <hannes@xxxxxxxxxxx> writes: > > > On Sat, Jun 09, 2012 at 02:29:59PM +0530, Aneesh Kumar K.V wrote: > >> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > >> > >> This adds necessary charge/uncharge calls in the HugeTLB code. We do > >> hugetlb cgroup charge in page alloc and uncharge in compound page destructor. > >> > >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > >> --- > >> mm/hugetlb.c | 16 +++++++++++++++- > >> mm/hugetlb_cgroup.c | 7 +------ > >> 2 files changed, 16 insertions(+), 7 deletions(-) > >> > >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c > >> index bf79131..4ca92a9 100644 > >> --- a/mm/hugetlb.c > >> +++ b/mm/hugetlb.c > >> @@ -628,6 +628,8 @@ static void free_huge_page(struct page *page) > >> BUG_ON(page_mapcount(page)); > >> > >> spin_lock(&hugetlb_lock); > >> + hugetlb_cgroup_uncharge_page(hstate_index(h), > >> + pages_per_huge_page(h), page); > > > > hugetlb_cgroup_uncharge_page() takes the hugetlb_lock, no? > > Yes, But this patch also modifies it to not take the lock, because we > hold spin_lock just below in the call site. I didn't want to drop the > lock and take it again. Sorry, I missed that. > > It's quite hard to review code that is split up like this. Please > > always keep the introduction of new functions in the same patch that > > adds the callsite(s). > > One of the reason I split the charge/uncharge routines and the callers > in separate patches is to make it easier for review. Irrespective of > the call site charge/uncharge routines should be correct with respect > to locking and other details. What I did in this patch is a small > optimization of avoiding dropping and taking the lock again. May be the > right approach would have been to name it __hugetlb_cgroup_uncharge_page > and make sure the hugetlb_cgroup_uncharge_page still takes spin_lock. > But then we don't have any callers for that. I think this makes it needlessly complicated and there is no correct or incorrect locking in (initially) dead code :-) The callsites are just a few lines. It's harder to review if you introduce an API and then change it again mid-patchset. If there are no callers for a function that grabs the lock itself, don't add it. Just add a note to the kerneldoc that explains the requirement or put VM_BUG_ON(!spin_is_locked(&hugetlb_lock)); in there or so. -- 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>