Re: [PATCH v3 3/4] mm: cma: add list of currently allocated CMA buffers to debugfs

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Stefan Strogin <s.strogin@partner.samsung.com> writes:

> Hi Aneesh,
>
> On 03/03/15 12:16, Aneesh Kumar K.V wrote:
>> Stefan Strogin <s.strogin@partner.samsung.com> writes:
>> 
>>> When CONFIG_CMA_BUFFER_LIST is configured a file is added to debugfs:
>>> /sys/kernel/debug/cma/cma-<N>/buffers contains a list of currently allocated
>>> CMA buffers for each CMA region (N stands for number of CMA region).
>>>
>>> Format is:
>>> <base_phys_addr> - <end_phys_addr> (<size> kB), allocated by <PID> (<comm>)
>>>
>>> When CONFIG_CMA_ALLOC_STACKTRACE is configured then stack traces are saved when
>>> the allocations are made. The stack traces are added to cma/cma-<N>/buffers
>>> for each buffer list entry.
>>>
>>> Example:
>>>
>>> root@debian:/sys/kernel/debug/cma# cat cma-0/buffers
>>> 0x2f400000 - 0x2f417000 (92 kB), allocated by pid 1 (swapper/0)
>>>  [<c1142c4b>] cma_alloc+0x1bb/0x200
>>>  [<c143d28a>] dma_alloc_from_contiguous+0x3a/0x40
>>>  [<c10079d9>] dma_generic_alloc_coherent+0x89/0x160
>>>  [<c14456ce>] dmam_alloc_coherent+0xbe/0x100
>>>  [<c1487312>] ahci_port_start+0xe2/0x210
>>>  [<c146e0e0>] ata_host_start.part.28+0xc0/0x1a0
>>>  [<c1473650>] ata_host_activate+0xd0/0x110
>>>  [<c14881bf>] ahci_host_activate+0x3f/0x170
>>>  [<c14854e4>] ahci_init_one+0x764/0xab0
>>>  [<c12e415f>] pci_device_probe+0x6f/0xd0
>>>  [<c14378a8>] driver_probe_device+0x68/0x210
>>>  [<c1437b09>] __driver_attach+0x79/0x80
>>>  [<c1435eef>] bus_for_each_dev+0x4f/0x80
>>>  [<c143749e>] driver_attach+0x1e/0x20
>>>  [<c1437197>] bus_add_driver+0x157/0x200
>>>  [<c14381bd>] driver_register+0x5d/0xf0
>>> <...>
>> 
>> A perf record -g will also give this information right ? To use this
>> feature, one need to recompile the kernel anyway. So why not assume that
>> user can always rerun the test with perf record -g and find the cma
>> allocation point stack trace ?
>> 
>> -aneesh
>> 
>
> Excuse me for the delay.
> I thought that 'perf record <command>' gathers data only for a command
> that it runs, does it? But we want to have information about all the
> allocations and releases from the boot time. 

>From boot time makes it interesting. Otherwise you could use perf
record. For ex:

./perf record -e kmem:kmalloc -g -a 
./perf script

jbd2/dm-3-8  7666 [000]  4666.621521: kmem:kmalloc: call_site=c0000000003ce108 ptr=0xc000000fcd646360 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_NOFS|GFP_ZERO
                  27f1dc .__kmalloc (/boot/vmlinux)
                       0 [unknown] ([unknown])
                  3de108 .ext4_find_extent (/boot/vmlinux)
                  3e4038 .ext4_ext_map_blocks (/boot/vmlinux)
                  3ab388 .ext4_map_blocks (/boot/vmlinux)
                  3ab970 ._ext4_get_block (/boot/vmlinux)
                  2df7e0 .generic_block_bmap (/boot/vmlinux)
                  3a7f4c .ext4_bmap (/boot/vmlinux)
                  2ba744 .bmap (/boot/vmlinux)
                  4293d4 .jbd2_journal_bmap (/boot/vmlinux)
                  41df84 .jbd2_journal_commit_transaction (/boot/vmlinux)
                  427620 .kjournald2 (/boot/vmlinux)
                   fbfa4 .kthread (/boot/vmlinux)
                   19568 .ret_from_kernel_thread (/boot/vmlinux)

....

>IMHO it would be more
> reasonable to use ftrace for that. But after all the patch enables to
> see not a history of allocations and deallocations but a current state
> of CMA region.
> As to recompilation, for example in our division this feature is enabled
> by default among other CONFIG_*_DEBUG features in debug versions of kernel.