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Date: Mon, 24 Apr 2017 14:12:30 -0400 From: Jérôme Glisse <jglisse@...hat.com> To: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org Cc: John Hubbard <jhubbard@...dia.com>, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, David Nellans <dnellans@...dia.com>, Jérôme Glisse <jglisse@...hat.com>, Ross Zwisler <ross.zwisler@...ux.intel.com> Subject: [HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2 Move page reference decrement of ZONE_DEVICE from put_page() to put_zone_device_page() this does not affect non ZONE_DEVICE page. Doing this allow to catch when a ZONE_DEVICE page refcount reach 1 which means the device is no longer reference by any one (unlike page from other zone, ZONE_DEVICE page refcount never reach 0). This patch is just a preparatory patch for HMM. Changes since v1: - commit message Signed-off-by: Jérôme Glisse <jglisse@...hat.com> Reviewed-by: Dan Williams <dan.j.williams@...el.com> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com> --- include/linux/mm.h | 14 +++++++++++--- kernel/memremap.c | 6 ++++++ 2 files changed, 17 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index c82e8db..022423c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -821,11 +821,19 @@ static inline void put_page(struct page *page) { page = compound_head(page); + /* + * ZONE_DEVICE pages should never have their refcount reach 0 (this + * would be a bug), so call page_ref_dec() in put_zone_device_page() + * to decrement page refcount and skip __put_page() here, as this + * would worsen things if a ZONE_DEVICE had a refcount bug. + */ + if (unlikely(is_zone_device_page(page))) { + put_zone_device_page(page); + return; + } + if (put_page_testzero(page)) __put_page(page); - - if (unlikely(is_zone_device_page(page))) - put_zone_device_page(page); } #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) diff --git a/kernel/memremap.c b/kernel/memremap.c index ea714ee..97ef676 100644 --- a/kernel/memremap.c +++ b/kernel/memremap.c @@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page); void put_zone_device_page(struct page *page) { + /* + * ZONE_DEVICE page refcount should never reach 0 and never be freed + * to kernel memory allocator. + */ + page_ref_dec(page); + put_dev_pagemap(page->pgmap); } EXPORT_SYMBOL(put_zone_device_page); -- 2.9.3
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