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Date: Tue, 5 Sep 2017 19:13:15 +0200
From: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To: Jérôme Glisse <jglisse@...hat.com>,
akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Cc: John Hubbard <jhubbard@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
David Nellans <dnellans@...dia.com>,
Balbir Singh <bsingharora@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
cgroups@...r.kernel.org
Subject: Re: [HMM-v25 10/19] mm/memcontrol: support MEMORY_DEVICE_PRIVATE v4
On 17/08/2017 02:05, Jérôme Glisse wrote:
> HMM pages (private or public device pages) are ZONE_DEVICE page and
> thus need special handling when it comes to lru or refcount. This
> patch make sure that memcontrol properly handle those when it face
> them. Those pages are use like regular pages in a process address
> space either as anonymous page or as file back page. So from memcg
> point of view we want to handle them like regular page for now at
> least.
>
> Changed since v3:
> - remove public support and move those chunk to separate patch
> Changed since v2:
> - s/host/public
> Changed since v1:
> - s/public/host
> - add comments explaining how device memory behave and why
>
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Acked-by: Balbir Singh <bsingharora@...il.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: cgroups@...r.kernel.org
> ---
> kernel/memremap.c | 1 +
> mm/memcontrol.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 49 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 398630c1fba3..f42d7483e886 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -492,6 +492,7 @@ void put_zone_device_private_page(struct page *page)
> __ClearPageWaiters(page);
>
> page->mapping = NULL;
> + mem_cgroup_uncharge(page);
>
> page->pgmap->page_free(page, page->pgmap->data);
> } else if (!count)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 604fb3ca8028..977d1cf3493a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4407,12 +4407,13 @@ enum mc_target_type {
> MC_TARGET_NONE = 0,
> MC_TARGET_PAGE,
> MC_TARGET_SWAP,
> + MC_TARGET_DEVICE,
> };
>
> static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
> unsigned long addr, pte_t ptent)
> {
> - struct page *page = vm_normal_page(vma, addr, ptent);
> + struct page *page = _vm_normal_page(vma, addr, ptent, true);
Hi Jérôme,
As _vm_normal_page() is defined later in the patch 18, so this patch should
break the bisectability.
Cheers,
Laurent.
>
> if (!page || !page_mapped(page))
> return NULL;
> @@ -4429,7 +4430,7 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
> return page;
> }
>
> -#ifdef CONFIG_SWAP
> +#if defined(CONFIG_SWAP) || defined(CONFIG_DEVICE_PRIVATE)
> static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
> pte_t ptent, swp_entry_t *entry)
> {
> @@ -4438,6 +4439,23 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
>
> if (!(mc.flags & MOVE_ANON) || non_swap_entry(ent))
> return NULL;
> +
> + /*
> + * Handle MEMORY_DEVICE_PRIVATE which are ZONE_DEVICE page belonging to
> + * a device and because they are not accessible by CPU they are store
> + * as special swap entry in the CPU page table.
> + */
> + if (is_device_private_entry(ent)) {
> + page = device_private_entry_to_page(ent);
> + /*
> + * MEMORY_DEVICE_PRIVATE means ZONE_DEVICE page and which have
> + * a refcount of 1 when free (unlike normal page)
> + */
> + if (!page_ref_add_unless(page, 1, 1))
> + return NULL;
> + return page;
> + }
> +
> /*
> * Because lookup_swap_cache() updates some statistics counter,
> * we call find_get_page() with swapper_space directly.
> @@ -4598,6 +4616,12 @@ static int mem_cgroup_move_account(struct page *page,
> * 2(MC_TARGET_SWAP): if the swap entry corresponding to this pte is a
> * target for charge migration. if @target is not NULL, the entry is stored
> * in target->ent.
> + * 3(MC_TARGET_DEVICE): like MC_TARGET_PAGE but page is MEMORY_DEVICE_PRIVATE
> + * (so ZONE_DEVICE page and thus not on the lru). For now we such page is
> + * charge like a regular page would be as for all intent and purposes it is
> + * just special memory taking the place of a regular page.
> + *
> + * See Documentations/vm/hmm.txt and include/linux/hmm.h
> *
> * Called with pte lock held.
> */
> @@ -4626,6 +4650,8 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
> */
> if (page->mem_cgroup == mc.from) {
> ret = MC_TARGET_PAGE;
> + if (is_device_private_page(page))
> + ret = MC_TARGET_DEVICE;
> if (target)
> target->page = page;
> }
> @@ -4693,6 +4719,11 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
>
> ptl = pmd_trans_huge_lock(pmd, vma);
> if (ptl) {
> + /*
> + * Note their can not be MC_TARGET_DEVICE for now as we do not
> + * support transparent huge page with MEMORY_DEVICE_PUBLIC or
> + * MEMORY_DEVICE_PRIVATE but this might change.
> + */
> if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
> mc.precharge += HPAGE_PMD_NR;
> spin_unlock(ptl);
> @@ -4908,6 +4939,14 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> putback_lru_page(page);
> }
> put_page(page);
> + } else if (target_type == MC_TARGET_DEVICE) {
> + page = target.page;
> + if (!mem_cgroup_move_account(page, true,
> + mc.from, mc.to)) {
> + mc.precharge -= HPAGE_PMD_NR;
> + mc.moved_charge += HPAGE_PMD_NR;
> + }
> + put_page(page);
> }
> spin_unlock(ptl);
> return 0;
> @@ -4919,12 +4958,16 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> for (; addr != end; addr += PAGE_SIZE) {
> pte_t ptent = *(pte++);
> + bool device = false;
> swp_entry_t ent;
>
> if (!mc.precharge)
> break;
>
> switch (get_mctgt_type(vma, addr, ptent, &target)) {
> + case MC_TARGET_DEVICE:
> + device = true;
> + /* fall through */
> case MC_TARGET_PAGE:
> page = target.page;
> /*
> @@ -4935,7 +4978,7 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> */
> if (PageTransCompound(page))
> goto put;
> - if (isolate_lru_page(page))
> + if (!device && isolate_lru_page(page))
> goto put;
> if (!mem_cgroup_move_account(page, false,
> mc.from, mc.to)) {
> @@ -4943,7 +4986,8 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> /* we uncharge from mc.from later. */
> mc.moved_charge++;
> }
> - putback_lru_page(page);
> + if (!device)
> + putback_lru_page(page);
> put: /* get_mctgt_type() gets the page */
> put_page(page);
> break;
>
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