| Message ID | 20230221214344.609226-1-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/khugepaged: alloc_charge_hpage() take care of mem charge errors | expand |
On Wed, Feb 22, 2023 at 6:43 AM Peter Xu <peterx@redhat.com> wrote: > > If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). > Let alloc_charge_hpage() handle the error itself and clear hpage properly > if mem charge fails. > > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Yang Shi <shy828301@gmail.com> > Cc: David Stevens <stevensd@chromium.org> > Cc: stable@vger.kernel.org > Fixes: 9d82c69438d0 ("mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API") > Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: David Stevens <stevensd@chromium.org>
Hello, On Tue, Feb 21, 2023 at 04:43:44PM -0500, Peter Xu wrote: > If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). > Let alloc_charge_hpage() handle the error itself and clear hpage properly > if mem charge fails. I'm a bit confused by this patch. There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out. It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either. I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on. So I'm not sure I understand the benefit of this change.
On Wed, Feb 22, 2023 at 12:06:20PM -0500, Johannes Weiner wrote: > Hello, > > On Tue, Feb 21, 2023 at 04:43:44PM -0500, Peter Xu wrote: > > If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). > > Let alloc_charge_hpage() handle the error itself and clear hpage properly > > if mem charge fails. > > I'm a bit confused by this patch. > > There isn't anything wrong with calling mem_cgroup_uncharge() on an > uncharged page, functionally. It checks and bails out. Indeed, I didn't really notice there's zero side effect of calling that, sorry. In that case both "Fixes" and "Cc: stable" do not apply. > > It's an unnecessary call of course, but since it's an error path it's > also not a cost issue, either. > > I could see an argument for improving the code, but this is actually > more code, and the caller still has the uncharge-and-put branch anyway > for when the collapse fails later on. > > So I'm not sure I understand the benefit of this change. Yes, the benefit is having a clear interface for alloc_charge_hpage() with no prone to leaking huge page. The patch comes from a review for David's other patch here: https://lore.kernel.org/all/Y%2FU9fBxVJdhxiZ1v@x1n/ I've attached a new version just to reword and remove the inproper tags. Do you think that's acceptable? Thanks,
On Wed, Feb 22, 2023 at 12:38:36PM -0500, Peter Xu wrote: > On Wed, Feb 22, 2023 at 12:06:20PM -0500, Johannes Weiner wrote: > > Hello, > > > > On Tue, Feb 21, 2023 at 04:43:44PM -0500, Peter Xu wrote: > > > If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). > > > Let alloc_charge_hpage() handle the error itself and clear hpage properly > > > if mem charge fails. > > > > I'm a bit confused by this patch. > > > > There isn't anything wrong with calling mem_cgroup_uncharge() on an > > uncharged page, functionally. It checks and bails out. > > Indeed, I didn't really notice there's zero side effect of calling that, > sorry. In that case both "Fixes" and "Cc: stable" do not apply. > > > > > It's an unnecessary call of course, but since it's an error path it's > > also not a cost issue, either. > > > > I could see an argument for improving the code, but this is actually > > more code, and the caller still has the uncharge-and-put branch anyway > > for when the collapse fails later on. > > > > So I'm not sure I understand the benefit of this change. > > Yes, the benefit is having a clear interface for alloc_charge_hpage() with > no prone to leaking huge page. > > The patch comes from a review for David's other patch here: > > https://lore.kernel.org/all/Y%2FU9fBxVJdhxiZ1v@x1n/ Ah, that makes sense. Thanks for the context. > From 0595acbd688b60ff7b2821a073c0fe857a4ae0ee Mon Sep 17 00:00:00 2001 > From: Peter Xu <peterx@redhat.com> > Date: Tue, 21 Feb 2023 16:43:44 -0500 > Subject: [PATCH] mm/khugepaged: alloc_charge_hpage() take care of mem charge > errors > > If memory charge failed, instead of returning the hpage but with an error, > allow the function to cleanup the folio properly, which is normally what a > function should do in this case - either return successfully, or return > with no side effect of partial runs with an indicated error. > > This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily > with either anon or shmem path (even if it's safe to do so). > > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Yang Shi <shy828301@gmail.com> > Cc: David Stevens <stevensd@chromium.org> > Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 8dbc39896811..941d1c7ea910 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1063,12 +1063,19 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm, gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : GFP_TRANSHUGE); int node = hpage_collapse_find_target_node(cc); + struct folio *folio; if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask)) return SCAN_ALLOC_HUGE_PAGE_FAIL; - if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp))) + + folio = page_folio(*hpage); + if (unlikely(mem_cgroup_charge(folio, mm, gfp))) { + folio_put(folio); + *hpage = NULL; return SCAN_CGROUP_CHARGE_FAIL; + } count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC); + return SCAN_SUCCEED; }
If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails. Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Yang Shi <shy828301@gmail.com> Cc: David Stevens <stevensd@chromium.org> Cc: stable@vger.kernel.org Fixes: 9d82c69438d0 ("mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API") Signed-off-by: Peter Xu <peterx@redhat.com> --- mm/khugepaged.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)