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:

> 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