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Message-ID: <e262f198-4092-1228-13f5-a0d40b29dc6c@yandex-team.ru>
Date: Mon, 25 May 2020 18:58:16 +0300
From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To: Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] mm: dump_page: add debugfs file for dumping page state by
pfn
On 25/05/2020 18.35, Vlastimil Babka wrote:
> On 5/25/20 4:19 PM, Konstantin Khlebnikov wrote:
>> Tool 'page-types' could list pages mapped by process or file cache pages,
>> but it shows only limited amount of state exported via procfs.
>>
>> Let's employ existing helper dump_page() to reach remaining information:
>> writing pfn into /sys/kernel/debug/dump_page dumps state into kernel log.
>
> Yeah that's indeed useful, however I'm less sure if kernel log is the proper way
> to extract the data. For example IIRC with the page_owner file can "seek to pfn"
> to dump it, although that makes it somewhat harder to use.
>
> Or we could write pfn to one file and read the dump from another one? But that's
> not atomic.
>
> Perhaps if we could do something like "cat /sys/kernel/debug/dump_page/<pfn>"
> without all the pfns being actually listed in the dump_page directory with "ls"?
> Is that possible?
Too much code for me. =)
This could be kind of ftrace tracer which iterates over pages and dumps them,
but anyway looks ridiculously overengineered.
This one hack connects existing 'pagemap' with existing 'dump_page', so almost free.
For complicated cases there is gdb and special tool drgn https://github.com/osandov/drgn
Writing script which parses all that stuff from kernel log isn't big deal either.
I have one with 100+ lines regexp for all kinds of kernel splats.
Will publish when find time for polishing.
>
>> # echo 0x37c43c > /sys/kernel/debug/dump_page
>> # dmesg | tail -6
>> page:ffffcb0b0df10f00 refcount:1 mapcount:0 mapping:000000007755d3d9 index:0x30
>> 0xffffffffae4239e0 name:"libGeoIP.so.1.6.9"
>> flags: 0x200000000020014(uptodate|lru|mappedtodisk)
>> raw: 0200000000020014 ffffcb0b187fd288 ffffcb0b189e6248 ffff9528a04afe10
>> raw: 0000000000000030 0000000000000000 00000001ffffffff 0000000000000000
>> page dumped because: debugfs request
>>
>> With CONFIG_PAGE_OWNER=y shows also stacks for last page alloc and free:
>>
>> page:ffffea0018fff480 refcount:1 mapcount:1 mapping:0000000000000000 index:0x7f9f28f62
>> anon flags: 0x100000000080034(uptodate|lru|active|swapbacked)
>> raw: 0100000000080034 ffffea00184140c8 ffffea0018517d88 ffff8886076ba161
>> raw: 00000007f9f28f62 0000000000000000 0000000100000000 ffff888bfc79f000
>> page dumped because: debugfs request
>> page->mem_cgroup:ffff888bfc79f000
>> page_owner tracks the page as allocated
>> page last allocated via order 0, migratetype Movable, gfp_mask 0x100dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO)
>> prep_new_page+0x139/0x1a0
>> get_page_from_freelist+0xde9/0x14e0
>> __alloc_pages_nodemask+0x18b/0x360
>> alloc_pages_vma+0x7c/0x270
>> __handle_mm_fault+0xd40/0x12b0
>> handle_mm_fault+0xe7/0x1e0
>> do_page_fault+0x2d5/0x610
>> page_fault+0x2f/0x40
>> page last free stack trace:
>> free_pcp_prepare+0x11e/0x1c0
>> free_unref_page_list+0x71/0x180
>> release_pages+0x31e/0x480
>> tlb_flush_mmu+0x44/0x150
>> tlb_finish_mmu+0x3d/0x70
>> exit_mmap+0xdd/0x1a0
>> mmput+0x70/0x140
>> do_exit+0x33f/0xc40
>> do_group_exit+0x3a/0xa0
>> __x64_sys_exit_group+0x14/0x20
>> do_syscall_64+0x48/0x130
>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
>> ---
>> Documentation/admin-guide/mm/pagemap.rst | 3 +++
>> Documentation/vm/page_owner.rst | 10 ++++++++++
>> mm/debug.c | 27 +++++++++++++++++++++++++++
>> 3 files changed, 40 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
>> index 340a5aee9b80..663ad5490d72 100644
>> --- a/Documentation/admin-guide/mm/pagemap.rst
>> +++ b/Documentation/admin-guide/mm/pagemap.rst
>> @@ -205,3 +205,6 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
>> always 12 at most architectures). Since Linux 3.11 their meaning changes
>> after first clear of soft-dirty bits. Since Linux 4.2 they are used for
>> flags unconditionally.
>> +
>> +Page state could be dumped into kernel log by writing pfn in text form
>> +into /sys/kernel/debug/dump_page.
>> diff --git a/Documentation/vm/page_owner.rst b/Documentation/vm/page_owner.rst
>> index 0ed5ab8c7ab4..d4d4dc64c19d 100644
>> --- a/Documentation/vm/page_owner.rst
>> +++ b/Documentation/vm/page_owner.rst
>> @@ -88,3 +88,13 @@ Usage
>>
>> See the result about who allocated each page
>> in the ``sorted_page_owner.txt``.
>> +
>> +Notes
>> +=====
>> +
>> +To lookup pages in file cache or mapped in process you could use interface
>> +pagemap documented in Documentation/admin-guide/mm/pagemap.rst or tool
>> +page-types in the tools/vm directory.
>> +
>> +Page state could be dumped into kernel log by writing pfn in text form
>> +into /sys/kernel/debug/dump_page.
>> diff --git a/mm/debug.c b/mm/debug.c
>> index 2189357f0987..5803f2b63d95 100644
>> --- a/mm/debug.c
>> +++ b/mm/debug.c
>> @@ -14,6 +14,7 @@
>> #include <linux/migrate.h>
>> #include <linux/page_owner.h>
>> #include <linux/ctype.h>
>> +#include <linux/debugfs.h>
>>
>> #include "internal.h"
>>
>> @@ -147,6 +148,32 @@ void dump_page(struct page *page, const char *reason)
>> }
>> EXPORT_SYMBOL(dump_page);
>>
>> +#ifdef CONFIG_DEBUG_FS
>> +static int dump_page_set(void *data, u64 pfn)
>> +{
>> + struct page *page;
>> +
>> + if (!capable(CAP_SYS_ADMIN))
>> + return -EPERM;
>> +
>> + page = pfn_to_online_page(pfn);
>> + if (!page)
>> + return -ENXIO;
>> +
>> + dump_page(page, "debugfs request");
>> + return 0;
>> +}
>> +DEFINE_DEBUGFS_ATTRIBUTE(dump_page_fops, NULL, dump_page_set, "%llx\n");
>> +
>> +static int __init dump_page_debugfs(void)
>> +{
>> + debugfs_create_file_unsafe("dump_page", 0200, NULL, NULL,
>> + &dump_page_fops);
>> + return 0;
>> +}
>> +late_initcall(dump_page_debugfs);
>> +#endif /* CONFIG_DEBUG_FS */
>> +
>> #ifdef CONFIG_DEBUG_VM
>>
>> void dump_vma(const struct vm_area_struct *vma)
>>
>
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