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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=mjhj2u5N2VQjkVMXKD4fyYvkC7HKj8duQThh+7BzG+Mi51cSWK66hhU5uTqF2mUuN dA1g6KM8NKeRrzhAgLSscHJnP6tbmxun8z1HRSwJECUAOBtqsWMhGoHttcVQnoC6eT 9sbYtbEDx6j5Acdf7mRPJmoXBR7WRBCN7n4LF9m8= Message-ID: <3a25e7fd-84a7-49a6-92a3-96492fe5d2cc@arm.com> Date: Tue, 12 May 2026 16:19:05 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/9] mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one To: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260506094504.2588857-1-dev.jain@arm.com> <20260506094504.2588857-2-dev.jain@arm.com> <06029485-9e85-4d2d-a324-abba918eecf3@arm.com> <771a8ee7-0a7c-4d70-9e7a-cc08abebd4aa@kernel.org> <2a749617-d70a-4931-9aa3-c9b680783b82@arm.com> <575f7210-b325-489e-9937-afccf29753a3@kernel.org> Content-Language: en-US From: Dev Jain In-Reply-To: <575f7210-b325-489e-9937-afccf29753a3@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7CD6F4000A X-Stat-Signature: otjf513qp7cmxen5wiw1zgosgo4mmxbz X-Rspam-User: X-HE-Tag: 1778582958-686168 X-HE-Meta: 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 25VeUFwo Lej6eKtGDDr2IpESGW7LOyILRlNCrNifRAdO2k64jlYrdUJyJXOg/z/HEcUdkHk3AW1HGUX1FIDImF5bXLnBnOHAz3spX/D0G2tafaCqv4VevnsduoeyRty928NFokNMUmH1YrB8R+qRJQk6Sz1W8LZkI9aDwYdrNqaBWxKKTh8zpD3Zj1iLcgTEr7uEzlGDOjqFF/uupetheckxpP65xRSu7G34i9kFOmANzE5vnRX0WhsCr3zKJl6o8rchmRUsoAqMRHWVICe5H0M5Uie4S8PteYypwPEkd7m6o Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/05/26 1:47 pm, David Hildenbrand (Arm) wrote: > On 5/12/26 10:14, Dev Jain wrote: >> >> >> On 11/05/26 2:02 pm, David Hildenbrand (Arm) wrote: >>> On 5/11/26 10:18, Dev Jain wrote: >>>> >>>> >>>> >>>> At the point of this patch, batching is supported for lazyfree and file folios. >>>> make_device_exclusive does not operate on file folios. >>> >>> That makes sense. >>> >>> You write "In practice, device-exclusive PTEs imply a GUP pin on the folio, and >>> lazyfree unmapping aborts try_to_unmap_one() when it detects that >>> condition. ". >>> >>> But I don't think the get_user_page_vma_remote() will set the pte/folio dirty? >>> >>> And the pin is only temporary. The caller of make_device_exclusive() will >>> essentially immediately drop that reference. >>> >>> So can't we just hit that? >>> >>> 1) Mark PTE-mapped folio lazyfree. Folio+ptes are clean. Can still be writable. >>> >>> 2) Convert last PTE to device-exclusive. get_user_page_vma_remote() only need >>> writable ptes, not dirty ptes. Caller drops the reference. >>> >>> 3) try_to_unmap_one() >>> >>> >>> Note that make_device_exclusive() documents: "device-exclusive entries are >>> considered "clean" and "old" by core-mm. Device drivers must update the folio >>> state when informed by MMU notifiers." >>> >>> But if it wasn't dirtied, there should be nothing guaranteeing that MMU >>> notifiers will set the folio dirty when MMU notifiers are triggered. >> >> You are correct. >> >> I did some changes in hmm-tests.c, to mmap and fault in 64K folios, >> MADV_FREE them, then trigger make_device_exclusive() via hmm_dmirror_cmd() >> on the last 4K part of the mapping, then trigger reclaim. I get: >> >> >> [ 96.896674] added new 256 MB chunk (total 1 chunks, 256 MB) PFNs [0x800030000 0x800040000) >> [ 96.897857] added new 256 MB chunk (total 1 chunks, 256 MB) PFNs [0x800020000 0x800030000) >> [ 96.898181] HMM test module loaded. This is only for testing HMM. >> [ 97.136132] page: refcount:17 mapcount:1 mapping:0000000000000000 index:0xfffff7bf0 pfn:0xc1a00 >> [ 97.136160] head: order:4 mapcount:16 entire_mapcount:0 nr_pages_mapped:16 pincount:0 >> [ 97.136211] memcg:ffff00019d433040 >> [ 97.136219] anon flags: 0x1ffff000000085d(locked|referenced|uptodate|dirty|owner_2|head|node=0|zone=0|lastcpupid=0x1ffff|kasantag=0x0) >> [ 97.136264] raw: 01ffff000000085d dead000000000100 dead000000000122 ffff0000030f8781 >> [ 97.136391] raw: 0000000fffff7bf0 0000000000000000 0000001100000000 ffff00019d433040 >> [ 97.136587] head: 01ffff000000085d dead000000000100 dead000000000122 ffff0000030f8781 >> [ 97.136828] head: 0000000fffff7bf0 0000000000000000 0000001100000000 ffff00019d433040 >> [ 97.137083] head: 01ffff0000000a04 fffffdffc2068001 000000100000000f 00000000ffffffff >> [ 97.137090] head: ffffffff0000000f 0000000000000021 0000000000000000 0000000000000010 >> [ 97.137096] page dumped because: VM_WARN_ON_FOLIO(!((!!(((pte).pte) & (((pteval_t)(1)) << 0))) || ((((pte).pte) & ((((pteval_t)(1)) << 0) | >> ((((pteval_t)(1)) << 11)))) == ((((pteval_t)(1)) << 11))))) >> [ 97.137122] ------------[ cut here ]------------ >> [ 97.137125] WARNING: mm/internal.h:346 at folio_pte_batch+0x54/0x360, CPU#4: hmm-tests/2283 >> [ 97.137206] Modules linked in: test_hmm >> [ 97.137234] CPU: 4 UID: 0 PID: 2283 Comm: hmm-tests Not tainted 7.1.0-rc1+ #17 PREEMPT >> [ 97.137237] Hardware name: linux,dummy-virt (DT) >> [ 97.137238] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) >> [ 97.137247] pc : folio_pte_batch+0x54/0x360 >> [ 97.137253] lr : folio_pte_batch+0x54/0x360 >> [ 97.137254] sp : ffff80008e7a3490 >> [ 97.137263] x29: ffff80008e7a3490 x28: 0000000000000001 x27: 0000fffff7dff000 >> [ 97.137266] x26: ffff0000451ceff0 x25: ffff000040fcaf00 x24: 00000000c1a0f780 >> [ 97.137269] x23: 0000000000001000 x22: fffffdffc2068000 x21: fffffdffc2068000 >> [ 97.137272] x20: ffff0000451ceff8 x19: 0000000000000001 x18: 0000000000000010 >> [ 97.137274] x17: 3030303030303020 x16: 3030303030303030 x15: 5f6c617665747028 >> [ 97.137276] x14: 282828207c202930 x13: 29312829745f6c61 x12: 7665747028282828 >> [ 97.137277] x11: 2929292929313120 x10: ffff8000838feb80 x9 : ffff800080287cb8 >> [ 97.137280] x8 : 3fffffffffffefff x7 : ffff8000838feb80 x6 : 0000000000000000 >> [ 97.137281] x5 : ffff0002fe74a0c8 x4 : 0000000000000000 x3 : 0000000000000000 >> [ 97.137282] x2 : 0000000000000000 x1 : ffff00014e120000 x0 : 00000000000000bb >> [ 97.137284] Call trace: >> [ 97.137285] folio_pte_batch+0x54/0x360 (P) >> [ 97.137288] folio_referenced_one+0x398/0x638 >> [ 97.137295] rmap_walk_anon+0x100/0x250 >> [ 97.137296] folio_referenced+0x17c/0x248 >> [ 97.137297] shrink_folio_list+0xf38/0x1968 >> [ 97.137307] shrink_lruvec+0x610/0xae8 >> [ 97.137311] shrink_node+0x218/0x888 >> [ 97.137314] __node_reclaim.constprop.0+0x98/0x328 >> [ 97.137318] user_proactive_reclaim+0x2b0/0x350 >> [ 97.137320] reclaim_store+0x3c/0x60 >> [ 97.137321] dev_attr_store+0x20/0x40 >> [ 97.137338] sysfs_kf_write+0x84/0xa8 >> [ 97.137351] kernfs_fop_write_iter+0x130/0x1c8 >> [ 97.137352] vfs_write+0x2c0/0x370 >> [ 97.137360] ksys_write+0x74/0x118 >> [ 97.137362] __arm64_sys_write+0x24/0x38 >> [ 97.137363] invoke_syscall+0x5c/0x120 >> [ 97.137374] el0_svc_common.constprop.0+0x48/0xf8 >> [ 97.137376] do_el0_svc+0x28/0x40 >> [ 97.137377] el0_svc+0x38/0x168 >> [ 97.137396] el0t_64_sync_handler+0xa0/0xe8 >> [ 97.137398] el0t_64_sync+0x1a4/0x1a8 >> [ 97.137400] ---[ end trace 0000000000000000 ]--- >> >> the warning happens in folio_referenced_one -> folio_pte_batch -> !pte_present(). >> Not sure why it happens in folio_referenced_one instead of try_to_unmap_one. >> >> I set nr_pages = 1 at the start of the pvmw walk in try_to_unmap_one and this >> goes away. >> >> Will send this as a separate fix patch. > > Awesome, thanks! (CC stable) Okay I think there is another bug. In folio_referenced_one, if (folio_test_large(folio)) { unsigned long end_addr = pmd_addr_end(address, vma->vm_end); unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT; pte_t pteval = ptep_get(pvmw.pte); nr = folio_pte_batch(folio, pvmw.pte, pteval, max_nr); } There is no pte_present(pteval) check here. We will encounter a non-present entry in folio_pte_batch(), giving the trace above. >