Johannes Weiner <hannes@xxxxxxxxxxx> writes: > 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. > I will fold the patches. > 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. That is excellent. I will add kerneldoc and VM_BUG_ON. -aneesh -- 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>