Re: [PATCH 0/4] mm: cma: add some debug information for CMA

[Joonsoo Kim]

On Fri, Feb 13, 2015 at 01:15:40AM +0300, Stefan Strogin wrote:
> Hi all.
> 
> Sorry for the long delay. Here is the second attempt to add some facility
> for debugging CMA (the first one was "mm: cma: add /proc/cmainfo" [1]).
> 
> This patch set is based on v3.19 and Sasha Levin's patch set
> "mm: cma: debugfs access to CMA" [2].
> It is also available on git:
> git://github.com/stefanstrogin/cmainfo -b cmainfo-v2
> 
> We want an interface to see a list of currently allocated CMA buffers and
> some useful information about them (like /proc/vmallocinfo but for physically
> contiguous buffers allocated with CMA).
> 
> Here is an example use case when we need it. We want a big (megabytes)
> CMA buffer to be allocated in runtime in default CMA region. If someone
> already uses CMA then the big allocation can fail. If it happens then with
> such an interface we could find who used CMA at the moment of failure, who
> caused fragmentation (possibly ftrace also would be helpful here) and so on.

Hello,

So, I'm not sure that information about allocated CMA buffer is really
needed to solve your problem. You just want to know who uses default CMA
region and you can know it by adding tracepoint in your 4/4 patch. We
really need this custom allocation tracer? What can we do more with
this custom tracer to solve your problem? Could you more specific
about your problem and how to solve it by using this custom tracer?

> 
> These patches add some files to debugfs when CONFIG_CMA_DEBUGFS is enabled.

If this tracer is justifiable, I think that making it conditional is
better than just enabling always on CONFIG_CMA_DEBUGFS. Some users
don't want to this feature although they enable CONFIG_CMA_DEBUGFS.

Thanks.

> 
> /sys/kernel/debug/cma/cma-<N>/buffers contains a list of currently allocated
> CMA buffers for each CMA region. Stacktrace saved at the moment of allocation
> is used to see who and whence allocated each buffer [3].
> 
> cma/cma-<N>/used and cma/cma-<N>/maxchunk are added to show used size and
> the biggest free chunk in each CMA region.
> 
> Also added trace events for cma_alloc() and cma_release().
> 
> Changes from "mm: cma: add /proc/cmainfo" [1]:
> - Rebased on v3.19 and Sasha Levin's patch set [2].
> - Moved debug code from cma.c to cma_debug.c.
> - Moved cmainfo to debugfs and splited it by CMA region.
> - Splited 'cmainfo' into 'buffers', 'used' and 'maxchunk'.
> - Used CONFIG_CMA_DEBUGFS instead of CONFIG_CMA_DEBUG.
> - Added trace events for cma_alloc() and cma_release().
> - Don't use seq_files.
> - A small change of debug output in cma_release().
> - cma_buffer_list_del() now supports releasing chunks which ranges don't match
>   allocations. E.g. we have buffer1: [0x0, 0x1], buffer2: [0x2, 0x3], then
>   cma_buffer_list_del(cma, 0x1 /*or 0x0*/, 1 /*(or 2 or 3)*/) should work.
> - Various small changes.
> 
> 
> [1] https://lkml.org/lkml/2014/12/26/95
> 
> [2] https://lkml.org/lkml/2015/1/28/755
> 
> [3] E.g.
> 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
> <...> 
> 0x2f41b000 - 0x2f41c000 (4 kB), allocated by pid 1264 (NetworkManager)
>  [<c1142c4b>] cma_alloc+0x1bb/0x200
>  [<c143d28a>] dma_alloc_from_contiguous+0x3a/0x40
>  [<c10079d9>] dma_generic_alloc_coherent+0x89/0x160
>  [<c14c5d13>] e1000_setup_all_tx_resources+0x93/0x540
>  [<c14c8021>] e1000_open+0x31/0x120
>  [<c16264cf>] __dev_open+0x9f/0x130
>  [<c16267ce>] __dev_change_flags+0x8e/0x150
>  [<c16268b8>] dev_change_flags+0x28/0x60
>  [<c1633ee0>] do_setlink+0x2a0/0x760
>  [<c1634acb>] rtnl_newlink+0x60b/0x7b0
>  [<c16314f4>] rtnetlink_rcv_msg+0x84/0x1f0
>  [<c164b58e>] netlink_rcv_skb+0x8e/0xb0
>  [<c1631461>] rtnetlink_rcv+0x21/0x30
>  [<c164af7a>] netlink_unicast+0x13a/0x1d0
>  [<c164b250>] netlink_sendmsg+0x240/0x3e0
>  [<c160cbfd>] do_sock_sendmsg+0xbd/0xe0
> <...>
> 
> 
> Dmitry Safonov (1):
>   mm: cma: add functions to get region pages counters
> 
> Stefan Strogin (3):
>   mm: cma: add currently allocated CMA buffers list to debugfs
>   mm: cma: add number of pages to debug message in cma_release()
>   mm: cma: add trace events to debug physically-contiguous memory
>     allocations
> 
>  include/linux/cma.h        |  11 +++
>  include/trace/events/cma.h |  57 +++++++++++++++
>  mm/cma.c                   |  46 +++++++++++-
>  mm/cma.h                   |  16 +++++
>  mm/cma_debug.c             | 169 ++++++++++++++++++++++++++++++++++++++++++++-
>  5 files changed, 297 insertions(+), 2 deletions(-)
>  create mode 100644 include/trace/events/cma.h
> 
> -- 
> 2.1.0
> 
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