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Mon, 9 Mar 2020 09:21:43 +0000 (UTC) Received: from [10.36.118.32] (unknown [10.36.118.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id 13F3528980; Mon, 9 Mar 2020 09:21:35 +0000 (UTC) Subject: Re: [PATCH -V3] mm: Add PageLayzyFree() helper functions for MADV_FREE To: "Huang, Ying" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen , Mel Gorman , Vlastimil Babka , Zi Yan , Michal Hocko , Peter Zijlstra , Minchan Kim , Johannes Weiner , Hugh Dickins References: <20200309021744.1309482-1-ying.huang@intel.com> <68360241-eb18-b3d8-bf6f-4dbbed258ee6@redhat.com> <87r1y1yjll.fsf@yhuang-dev.intel.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <23076072-7875-cabf-768f-ce27cba3480d@redhat.com> Date: Mon, 9 Mar 2020 10:21:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <87r1y1yjll.fsf@yhuang-dev.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09.03.20 10:15, Huang, Ying wrote: > David Hildenbrand writes: > >> On 09.03.20 03:17, Huang, Ying wrote: >>> From: Huang Ying >>> >>> Now PageSwapBacked() is used as the helper function to check whether >>> pages have been freed lazily via MADV_FREE. This isn't very obvious. >>> So Dave suggested to add PageLazyFree() family helper functions to >>> improve the code readability. >>> >>> Signed-off-by: "Huang, Ying" >>> Suggested-by: Dave Hansen >>> Cc: David Hildenbrand >>> Cc: Mel Gorman >>> Cc: Vlastimil Babka >>> Cc: Zi Yan >>> Cc: Michal Hocko >>> Cc: Peter Zijlstra >>> Cc: Minchan Kim >>> Cc: Johannes Weiner >>> Cc: Hugh Dickins >>> --- >>> Changelog: >>> >>> v3: >>> >>> - Improved comments, Thanks David Hildenbrand! >>> >>> - Use the helper function in /proc/PID/smaps lazyfree reporting. >>> >>> v2: >>> >>> - Avoid code bloat via removing VM_BUG_ON_PAGE(), which doesn't exist >>> in the original code. Now there is no any text/data/bss size >>> change. >>> >>> - Fix one wrong replacement in try_to_unmap_one(). >>> >>> --- >>> fs/proc/task_mmu.c | 2 +- >>> include/linux/page-flags.h | 25 +++++++++++++++++++++++++ >>> mm/rmap.c | 4 ++-- >>> mm/swap.c | 11 +++-------- >>> mm/vmscan.c | 7 +++---- >>> 5 files changed, 34 insertions(+), 15 deletions(-) >>> >>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c >>> index 3ba9ae83bff5..3458d5711e57 100644 >>> --- a/fs/proc/task_mmu.c >>> +++ b/fs/proc/task_mmu.c >>> @@ -471,7 +471,7 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, >>> */ >>> if (PageAnon(page)) { >>> mss->anonymous += size; >>> - if (!PageSwapBacked(page) && !dirty && !PageDirty(page)) >>> + if (__PageLazyFree(page) && !dirty && !PageDirty(page)) >>> mss->lazyfree += size; >>> } >>> >>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >>> index 49c2697046b9..bb26f74cbe8e 100644 >>> --- a/include/linux/page-flags.h >>> +++ b/include/linux/page-flags.h >>> @@ -498,6 +498,31 @@ static __always_inline int PageKsm(struct page *page) >>> TESTPAGEFLAG_FALSE(Ksm) >>> #endif >>> >>> +/* >>> + * For pages freed lazily via MADV_FREE. Lazyfree pages are clean >>> + * anonymous pages. They don't have PG_swapbacked set, to distinguish >>> + * them from normal anonymous pages. >>> + */ >>> +static __always_inline int __PageLazyFree(struct page *page) >>> +{ >>> + return !PageSwapBacked(page); >>> +} >>> + >>> +static __always_inline int PageLazyFree(struct page *page) >>> +{ >>> + return PageAnon(page) && __PageLazyFree(page); >>> +} >>> + >>> +static __always_inline void SetPageLazyFree(struct page *page) >>> +{ >>> + ClearPageSwapBacked(page); >>> +} >>> + >>> +static __always_inline void ClearPageLazyFree(struct page *page) >>> +{ >>> + SetPageSwapBacked(page); >>> +} >>> + >>> u64 stable_page_flags(struct page *page); >>> >>> static inline int PageUptodate(struct page *page) >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 1c02adaa233e..6ec96c8e7826 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1609,7 +1609,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> } >>> >>> /* MADV_FREE page check */ >>> - if (!PageSwapBacked(page)) { >>> + if (__PageLazyFree(page)) { >>> if (!PageDirty(page)) { >>> /* Invalidate as we cleared the pte */ >>> mmu_notifier_invalidate_range(mm, >>> @@ -1623,7 +1623,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> * discarded. Remap the page to page table. >>> */ >>> set_pte_at(mm, address, pvmw.pte, pteval); >>> - SetPageSwapBacked(page); >>> + ClearPageLazyFree(page); >>> ret = false; >>> page_vma_mapped_walk_done(&pvmw); >>> break; >>> diff --git a/mm/swap.c b/mm/swap.c >>> index c1d3ca80ea10..d83f2cd4cdb8 100644 >>> --- a/mm/swap.c >>> +++ b/mm/swap.c >>> @@ -563,7 +563,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec, >>> static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, >>> void *arg) >>> { >>> - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && >>> + if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) && >>> !PageSwapCache(page) && !PageUnevictable(page)) { >>> bool active = PageActive(page); >>> >>> @@ -571,12 +571,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, >>> LRU_INACTIVE_ANON + active); >>> ClearPageActive(page); >>> ClearPageReferenced(page); >>> - /* >>> - * lazyfree pages are clean anonymous pages. They have >>> - * SwapBacked flag cleared to distinguish normal anonymous >>> - * pages >>> - */ >>> - ClearPageSwapBacked(page); >>> + SetPageLazyFree(page); >>> add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE); >>> >>> __count_vm_events(PGLAZYFREE, hpage_nr_pages(page)); >>> @@ -678,7 +673,7 @@ void deactivate_page(struct page *page) >>> */ >>> void mark_page_lazyfree(struct page *page) >>> { >>> - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && >>> + if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) && >>> !PageSwapCache(page) && !PageUnevictable(page)) { >>> struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs); >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index eca49a1c2f68..40bb41ada2d2 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1043,8 +1043,7 @@ static void page_check_dirty_writeback(struct page *page, >>> * Anonymous pages are not handled by flushers and must be written >>> * from reclaim context. Do not stall reclaim based on them >>> */ >>> - if (!page_is_file_cache(page) || >>> - (PageAnon(page) && !PageSwapBacked(page))) { >>> + if (!page_is_file_cache(page) || PageLazyFree(page)) { >>> *dirty = false; >>> *writeback = false; >>> return; >>> @@ -1235,7 +1234,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >>> * Try to allocate it some swap space here. >>> * Lazyfree page could be freed directly >>> */ >>> - if (PageAnon(page) && PageSwapBacked(page)) { >>> + if (PageAnon(page) && !__PageLazyFree(page)) { >>> if (!PageSwapCache(page)) { >>> if (!(sc->gfp_mask & __GFP_IO)) >>> goto keep_locked; >>> @@ -1411,7 +1410,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >>> } >>> } >>> >>> - if (PageAnon(page) && !PageSwapBacked(page)) { >>> + if (PageLazyFree(page)) { >>> /* follow __remove_mapping for reference */ >>> if (!page_ref_freeze(page, 1)) >>> goto keep_locked; >>> >> >> I still prefer something like >> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index fd6d4670ccc3..7538501230bd 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h >> @@ -63,6 +63,10 @@ >> * page_waitqueue(page) is a wait queue of all tasks waiting for the page >> * to become unlocked. >> * >> + * PG_swapbacked used with anonymous pages (PageAnon()) indicates that a >> + * page is backed by swap. Anonymous pages without PG_swapbacked are >> + * pages that can be lazily freed (e.g., MADV_FREE) on demand. >> + * >> * PG_uptodate tells whether the page's contents is valid. When a read >> * completes, the page becomes uptodate, unless a disk I/O error happened. >> * > > Why not just send a formal patch? So Andrew can just pick anything he > likes. I am totally OK with that. Because you're working on cleaning this up. > >> and really don't like the use of !__PageLazyFree() instead of PageSwapBacked(). > > If adopted, !__PageLazyFree() should only be used in the context where > we really want to check whether pages are freed lazily. Otherwise, > PageSwapBacked() should be used. > Yeah, and once again, personally, I don't like this approach. E.g., ClearPageLazyFree() sets PG_swapbacked. You already have to be aware that this is a single flag being used in the background and what the implications are. IMHO, in no way better than the current approach. I prefer better documentation instead. But I am just a reviewer and not a maintainer, so it's just my 2 cents. -- Thanks, David / dhildenb