| Message ID | alpine.LSU.2.11.2008301358020.5954@eggly.anvils (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: fixes to past from future testing | expand |
On Sun, Aug 30, 2020 at 1:59 PM Hugh Dickins <hughd@google.com> wrote: > > In 5.8 some instances of memcg charging in do_swap_page() and unuse_pte() > were removed, on the understanding that swap cache is now already charged > at those points; but a case was missed, when ksm_might_need_to_copy() has > decided it must allocate a substitute page: such pages were never charged. > Fix it inside ksm_might_need_to_copy(). > > This was discovered by Alex Shi's prospective commit "mm/memcg: warning > on !memcg after readahead page charged". > > But there is a another surprise: this also fixes some rarer uncharged > PageAnon cases, when KSM is configured in, but has never been activated. > ksm_might_need_to_copy()'s anon_vma->root and linear_page_index() check > sometimes catches a case which would need to have been copied if KSM > were turned on. Or that's my optimistic interpretation (of my own old > code), but it leaves some doubt as to whether everything is working as > intended there - might it hint at rare anon ptes which rmap cannot find? > A question not easily answered: put in the fix for missed memcg charges. > > Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation") > Signed-off-by: Hugh Dickins <hughd@google.com> > Cc: stable@vger.kernel.org # v5.8 Reviewed-by: Shakeel Butt <shakeelb@google.com>
On Sun, Aug 30, 2020 at 01:59:35PM -0700, Hugh Dickins wrote: > In 5.8 some instances of memcg charging in do_swap_page() and unuse_pte() > were removed, on the understanding that swap cache is now already charged > at those points; but a case was missed, when ksm_might_need_to_copy() has > decided it must allocate a substitute page: such pages were never charged. > Fix it inside ksm_might_need_to_copy(). > > This was discovered by Alex Shi's prospective commit "mm/memcg: warning > on !memcg after readahead page charged". > > But there is a another surprise: this also fixes some rarer uncharged > PageAnon cases, when KSM is configured in, but has never been activated. > ksm_might_need_to_copy()'s anon_vma->root and linear_page_index() check > sometimes catches a case which would need to have been copied if KSM > were turned on. Or that's my optimistic interpretation (of my own old > code), but it leaves some doubt as to whether everything is working as > intended there - might it hint at rare anon ptes which rmap cannot find? > A question not easily answered: put in the fix for missed memcg charges. > > Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation") > Signed-off-by: Hugh Dickins <hughd@google.com> > Cc: stable@vger.kernel.org # v5.8 Acked-by: Johannes Weiner <hannes@cmpxchg.org>
--- 5.9-rc2/mm/ksm.c 2020-08-16 17:32:50.645506940 -0700 +++ linux/mm/ksm.c 2020-08-28 17:42:07.967278385 -0700 @@ -2582,6 +2582,10 @@ struct page *ksm_might_need_to_copy(stru return page; /* let do_swap_page report the error */ new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); + if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) { + put_page(new_page); + new_page = NULL; + } if (new_page) { copy_user_highpage(new_page, page, address, vma);
In 5.8 some instances of memcg charging in do_swap_page() and unuse_pte() were removed, on the understanding that swap cache is now already charged at those points; but a case was missed, when ksm_might_need_to_copy() has decided it must allocate a substitute page: such pages were never charged. Fix it inside ksm_might_need_to_copy(). This was discovered by Alex Shi's prospective commit "mm/memcg: warning on !memcg after readahead page charged". But there is a another surprise: this also fixes some rarer uncharged PageAnon cases, when KSM is configured in, but has never been activated. ksm_might_need_to_copy()'s anon_vma->root and linear_page_index() check sometimes catches a case which would need to have been copied if KSM were turned on. Or that's my optimistic interpretation (of my own old code), but it leaves some doubt as to whether everything is working as intended there - might it hint at rare anon ptes which rmap cannot find? A question not easily answered: put in the fix for missed memcg charges. Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation") Signed-off-by: Hugh Dickins <hughd@google.com> Cc: stable@vger.kernel.org # v5.8 --- mm/ksm.c | 4 ++++ 1 file changed, 4 insertions(+)