From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id 6AC846B02E0 for ; Fri, 26 Oct 2018 04:50:45 -0400 (EDT) Received: by mail-pf1-f198.google.com with SMTP id d7-v6so260443pfj.6 for ; Fri, 26 Oct 2018 01:50:45 -0700 (PDT) Received: from mailgw01.mediatek.com ([210.61.82.183]) by mx.google.com with ESMTPS id q5-v6si11052479pgg.105.2018.10.26.01.50.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Oct 2018 01:50:44 -0700 (PDT) Message-ID: <1540543834.21297.14.camel@mtkswgap22> Subject: Re: [PATCH] mm/page_owner: use vmalloc instead of kmalloc From: Miles Chen Date: Fri, 26 Oct 2018 16:50:34 +0800 In-Reply-To: <20181025192701.GK25444@bombadil.infradead.org> References: <1540492481-4144-1-git-send-email-miles.chen@mediatek.com> <20181025192701.GK25444@bombadil.infradead.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Matthias Brugger , linux-kernel@vger.kernel.org, linux-mm@kvack.org, wsd_upstream@mediatek.com, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org On Thu, 2018-10-25 at 12:27 -0700, Matthew Wilcox wrote: > On Fri, Oct 26, 2018 at 02:34:41AM +0800, miles.chen@mediatek.com wrote: > > The kbuf used by page owner is allocated by kmalloc(), > > which means it can use only normal memory and there might > > be a "out of memory" issue when we're out of normal memory. > > > > Use vmalloc() so we can also allocate kbuf from highmem > > on 32bit kernel. > > ... hang on, there's a bigger problem here. > > static const struct file_operations proc_page_owner_operations = { > .read = read_page_owner, > }; > > read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > { > ... > return print_page_owner(buf, count, pfn, page, > page_owner, handle); > } > > static ssize_t > print_page_owner(char __user *buf, size_t count, unsigned long pfn, > struct page *page, struct page_owner *page_owner, > depot_stack_handle_t handle) > {mount -t debugfs none /sys/kernel/debug/ > ... > kbuf = kmalloc(count, GFP_KERNEL); > > So I can force the kernel to make an arbitrary size allocation, triggering > OOMs and forcing swapping if I can get a file handle to this file. > The only saving grace is that (a) this is a debugfs file and (b) it's > root-only (mode 0400). Nevertheless, I feel some clamping is called > for here. Do we really need to output more than 4kB worth of text here? > I did a test on my device, the allocation count is 4096 and around 6xx bytes are used each print_page_owner() is called. It looks like that clamping the reading count to PAGE_SIZE is ok. The following output from print_page_owner() is 660 bytes long, I think PAGE_SIZE should be enough to print the information we need. Page allocated via order 0, mask 0x6200ca(GFP_HIGHUSER_MOVABLE) PFN 262199 type Movable Block 512 type Movable Flags 0x4003c(referenced| uptodate|dirty|lru|swapbacked) get_page_from_freelist+0x1580/0x1650 __alloc_pages_nodemask+0xcc/0xfa4 shmem_alloc_page+0xa4/0xc8 shmem_alloc_and_acct_page+0x138/0x2b8 shmem_getpage_gfp.isra.54+0x164/0xfc8 shmem_write_begin+0x84/0xcc generic_perform_write+0xe8/0x210 __generic_file_write_iter+0x1d4/0x230 generic_file_write_iter+0x184/0x2e8 new_sync_write+0x144/0x1c4 vfs_write+0x194/0x278 ksys_write+0x64/0xd4 xwrite+0x34/0x84 do_copy+0xf4/0x168 flush_buffer+0x68/0xec __gunzip+0x370/0x448