Re: [PATCH 5/5] scripts/gdb: Add meminfo command

[Jan Kiszka]

On 2016-01-20 12:15, Kieran Bingham wrote:
> Provide an equivalent of /proc/meminfo which should be available from
> core dumps, or crashed kernels. This should allow a debugger to identify
> if memory pressures were applicable in the instance of their issue
> 
> Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxx>
> ---
> 
> This command has proved to be much more difficult that I first thought it
> would be!
> 
> It also poses a couple of interesting issues, which is why I submit this
> patch in a much more unfinished form.

Yeah, seems so - see below ;)

> 
> The meminfo implementation at fs/proc/meminfo.c makes several function calls
> to collate information, which makes duplicating here more difficult.
> 
> I suspect the best option here is to not present lines of which we can not
> obtain accurate data for, (much better than presenting inaccurate information)
> 
> Would this go in agreement with you?

I didn't grab the use cases yet, so just a general suggestion: if the
inaccurate information may still have some value, you can mark it as
inaccurate and still print it.

> 
> Finally, do you have any ideas on the best way to manage code which
> is #ifdef'd on kernel config options? (#ifdef CONFIG_HIGHMEM for example).
> 
> In a similar vein to the constants.py, I considered that we could iterate all
> of the kernel configuration options and store them in a dictionary some how.
> 
> That may be awkward, however, and I wondered what ideas anyone had!

Why not convert the (relevant) configs inside constants.py into a
python variable? CONFIG_IS_ENABLED should make this easy.

> 
> 
>  scripts/gdb/linux/constants.py.in |  22 +++++
>  scripts/gdb/linux/proc.py         | 173 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 195 insertions(+)
> 
> diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
> index 739a15d2e984..306bd601ae4e 100644
> --- a/scripts/gdb/linux/constants.py.in
> +++ b/scripts/gdb/linux/constants.py.in
> @@ -12,8 +12,15 @@
>   *
>   */
>  
> +#include <asm/page.h>
> +#include <asm/pgtable.h>
> +#include <asm/thread_info.h>
> +
>  #include <linux/fs.h>
> +#include <linux/swap.h>
>  #include <linux/mount.h>
> +#include <linux/vmalloc.h>
> +
>  
>  /* We need to stringify expanded macros so that they can be parsed */
>  
> @@ -41,3 +48,18 @@ LX_MNT_NOATIME = MNT_NOATIME
>  LX_MNT_NODIRATIME = MNT_NODIRATIME
>  LX_MNT_RELATIME = MNT_RELATIME
>  
> +/* asm/page.h */
> +LX_PAGE_SHIFT = XSTRING(PAGE_SHIFT)
> +lx_page_shift = gdb.parse_and_eval(LX_PAGE_SHIFT)
> +
> +/* asm/thread_info.h */
> +LX_THREAD_SIZE = XSTRING(THREAD_SIZE)
> +lx_thread_size = gdb.parse_and_eval(LX_THREAD_SIZE)
> +
> +/* linux/vmalloc.h */
> +LX_VMALLOC_TOTAL = XSTRING(VMALLOC_TOTAL)
> +lx_vmalloc_total = gdb.parse_and_eval(LX_VMALLOC_TOTAL)
> +
> +/* linux/swap.h */
> +LX_MAX_SWAPFILES = XSTRING(MAX_SWAPFILES)
> +lx_max_swapfiles = gdb.parse_and_eval(LX_MAX_SWAPFILES)
> diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
> index b79ce2a33a3d..ac9e1aac2403 100644
> --- a/scripts/gdb/linux/proc.py
> +++ b/scripts/gdb/linux/proc.py
> @@ -206,3 +206,176 @@ values of that process namespace"""
>                          info_opts(MNT_INFO, m_flags)))
>  
>  LxMounts()
> +
> +
> +bdev_type = utils.CachedType("struct block_device")
> +
> +
> +class LxMeminfo(gdb.Command):
> +    """ Identify the memory usage, statistics, and availability
> +
> +Equivalent to cat /proc/meminfo on a running target """
> +
> +    def __init__(self):
> +        super(LxMeminfo, self).__init__("lx-meminfo", gdb.COMMAND_DATA)
> +
> +    def K(self, val):
> +        # Convert from PAGES to KB
> +        return int(val << (constants.lx_page_shift - 10))
> +
> +    def page_K(self, remote_value):
> +        # Obtain page value, and Convert from PAGES to KB
> +        val = int(gdb.parse_and_eval(remote_value))
> +        return self.K(val)
> +
> +    def gps(self, enum_zone_stat_item):
> +        # Access the Global Page State structure
> +        # I would prefer to read this structure in one go and then index
> +        # from the enum. But we can't determine the enum values with out
> +        # a call to GDB anyway so we may as well take the easy route and
> +        # get the value.
> +        remote_value = "vm_stat[" + enum_zone_stat_item + "].counter"
> +        return int(gdb.parse_and_eval(remote_value))
> +
> +    def gps_K(self, enum_zone_stat_item):
> +        return self.K(self.gps(enum_zone_stat_item))
> +
> +    def nr_blockdev_pages(self):
> +        bdevs_head = gdb.parse_and_eval("all_bdevs")
> +        pages = 0
> +        for bdev in lists.items(bdev_type, "bd_list", bdevs_head):
> +            pages += bdev['bd_inode']['i_mapping']['nrpages']
> +        return pages
> +
> +    def total_swapcache_pages(self):
> +        pages = 0
> +        for i in range(0, constants.lx_max_swapfiles):
> +            swap_space = "swapper_spaces[" + str(i) + "].nrpages"
> +            pages += int(gdb.parse_and_eval(swap_space))
> +        return pages
> +
> +    def vm_commit_limit(self, totalram_pages):
> +        overcommit = int(gdb.parse_and_eval("sysctl_overcommit_kbytes"))
> +        overcommit_ratio = int(gdb.parse_and_eval("sysctl_overcommit_ratio"))
> +        total_swap_pages = int(gdb.parse_and_eval("total_swap_pages"))
> +        hugetlb_total_pages = 0  # hugetlb_total_pages()!!
> +
> +        if overcommit:
> +            allowed = overcommit >> (constants.lx_page_shift - 10)
> +        else:
> +            allowed = ((totalram_pages - hugetlb_total_pages *
> +                       overcommit_ratio / 100))
> +
> +        allowed += total_swap_pages
> +        return allowed
> +
> +    # Main lx-meminfo command execution
> +    def invoke(self, arg, from_tty):
> +        totalram = int(gdb.parse_and_eval("totalram_pages"))
> +        freeram = self.gps("NR_FREE_PAGES")
> +        reclaimable = self.gps("NR_SLAB_RECLAIMABLE")
> +        unreclaimable = self.gps("NR_SLAB_UNRECLAIMABLE")
> +        slab = reclaimable + unreclaimable
> +        # for_each_zone(zone)
> +        #     wmark_low += zone->watermark[WMARK_LOW];
> +        wmark_low = 0   # Zone parsing is unimplemented
> +
> +        available = freeram - wmark_low
> +        available += reclaimable - min(reclaimable / 2, wmark_low)
> +
> +        bufferram = self.nr_blockdev_pages()

Something goes wrong here:

(gdb) lx-meminfo 
Traceback (most recent call last):
  File "/data/linux/build-dbg/scripts/gdb/linux/proc.py", line 286, in invoke
    bufferram = self.nr_blockdev_pages()
  File "/data/linux/build-dbg/scripts/gdb/linux/proc.py", line 246, in nr_blockdev_pages
    for bdev in lists.items(bdev_type, "bd_list", bdevs_head):
  File "/data/linux/build-dbg/scripts/gdb/linux/lists.py", line 26, in items
    yield utils.container_of(next_item, list_type, list_location)
  File "/data/linux/build-dbg/scripts/gdb/linux/utils.py", line 52, in container_of
    offset_of(typeobj, member)).cast(typeobj)
  File "/data/linux/build-dbg/scripts/gdb/linux/utils.py", line 46, in offset_of
    element = gdb.Value(0).cast(typeobj)
RuntimeError: Argument must be a type.
Error occurred in Python command: Argument must be a type.

If you need my kernel config to reproduce, just let me know.

> +        total_swapcache_pages = self.total_swapcache_pages()
> +
> +        file_pages = self.gps("NR_FILE_PAGES")
> +        cached = file_pages - total_swapcache_pages - bufferram
> +
> +        # LRU Pages
> +        active_pages_anon = self.gps("NR_ACTIVE_ANON")
> +        inactive_pages_anon = self.gps("NR_INACTIVE_ANON")
> +        active_pages_file = self.gps("NR_ACTIVE_FILE")
> +        inactive_pages_file = self.gps("NR_INACTIVE_FILE")
> +        unevictable_pages = self.gps("NR_UNEVICTABLE")
> +        active_pages = active_pages_anon + active_pages_file
> +        inactive_pages = inactive_pages_anon + inactive_pages_file
> +
> +        totalhigh = int(gdb.parse_and_eval("totalhigh_pages"))
> +        # We can't run this on a core dump file ...
> +        # if running target ()
> +        freehigh = int(gdb.parse_and_eval("nr_free_highpages()"))
> +        # else freehigh = 0
> +
> +        kernelstack = int(self.gps("NR_KERNEL_STACK") *
> +                          constants.lx_thread_size / 1024)
> +
> +        commitlimit = self.vm_commit_limit(totalram)
> +        committed_as = int(gdb.parse_and_eval("vm_committed_as.count"))
> +
> +        vmalloc_total = int(constants.lx_vmalloc_total >> 10)
> +
> +        gdb.write(
> +            "MemTotal:       {:8d} kB\n".format(self.K(totalram)) +
> +            "MemFree:        {:8d} kB\n".format(self.K(freeram)) +
> +            "MemAvailable:   {:8d} kB\n".format(self.K(available)) +
> +            "Buffers:        {:8d} kB\n".format(self.K(bufferram)) +
> +            "Cached:         {:8d} kB\n".format(self.K(cached)) +
> +            "SwapCached:     {:8d} kB\n".format(self.K(total_swapcache_pages)) +
> +            "Active:         {:8d} kB\n".format(self.K(active_pages)) +
> +            "Inactive:       {:8d} kB\n".format(self.K(inactive_pages)) +
> +            "Active(anon):   {:8d} kB\n".format(self.K(active_pages_anon)) +
> +            "Inactive(anon): {:8d} kB\n".format(self.K(inactive_pages_anon)) +
> +            "Active(file):   {:8d} kB\n".format(self.K(active_pages_file)) +
> +            "Inactive(file): {:8d} kB\n".format(self.K(inactive_pages_file)) +
> +            "Unevictable:    {:8d} kB\n".format(self.K(unevictable_pages)) +
> +            "Mlocked:        {:8d} kB\n".format(self.gps_K("NR_MLOCK"))
> +            )
> +        # ifdef CONFIG_HIGHMEM || core dump?
> +        gdb.write(
> +            "HighTotal:      {:8d} kB\n".format(self.K(totalhigh)) +
> +            "HighFree:       {:8d} kB\n".format(self.K(freehigh)) +
> +            "LowTotal:       {:8d} kB\n".format(self.K(totalram-totalhigh)) +
> +            "LowFree:        {:8d} kB\n".format(self.K(freeram-freehigh))
> +            )
> +        # endif
> +        # ifndef CONFIG_MMU
> +        # gdb.write(
> +        #    mmap_pages_allocated
> +        #    )
> +        # endif
> +        gdb.write(
> +            "SwapTotal:      {:8d} kB\n".format(self.K(0)) +
> +            "SwapFree:       {:8d} kB\n".format(self.K(0)) +
> +            "Dirty:          {:8d} kB\n".format(self.gps_K("NR_FILE_DIRTY")) +
> +            "Writeback:      {:8d} kB\n".format(self.gps_K("NR_WRITEBACK")) +
> +            "AnonPages:      {:8d} kB\n".format(self.gps_K("NR_ANON_PAGES")) +
> +            "Mapped:         {:8d} kB\n".format(self.gps_K("NR_FILE_MAPPED")) +
> +            "Shmem:          {:8d} kB\n".format(self.gps_K("NR_SHMEM")) +
> +            "Slab:           {:8d} kB\n".format(self.K(slab)) +
> +            "SReclaimable:   {:8d} kB\n".format(self.K(reclaimable)) +
> +            "SUnreclaim:     {:8d} kB\n".format(self.K(unreclaimable)) +
> +            "KernelStack:    {:8d} kB\n".format(kernelstack) +
> +            "PageTables:     {:8d} kB\n".format(self.gps_K("NR_PAGETABLE"))
> +            )
> +
> +        #  if CONFIG_QUICKLIST
> +        #   "Quicklists:     {:8d} kB\n".format(self.K(quicklist)))
> +
> +        gdb.write(
> +            "NFS_Unstable:   {:8d} kB\n".format(self.gps_K("NR_UNSTABLE_NFS")) +
> +            "Bounce:         {:8d} kB\n".format(self.gps_K("NR_BOUNCE")) +
> +            "WritebackTmp:   {:8d} kB\n".format(self.gps_K("NR_WRITEBACK_TEMP")) +
> +            "CommitLimit:    {:8d} kB\n".format(self.K(commitlimit)) +
> +            "Committed_AS:   {:8d} kB\n".format(self.K(committed_as)) +
> +            "VmallocTotal:   {:8d} kB\n".format(vmalloc_total) +
> +            "VmallocUsed:    {:8d} kB\n".format(0) +
> +            "VmallocChunk:   {:8d} kB\n".format(0)
> +            )
> +        # if CONFIG_MEMORY_FAILURE
> +        #   "HardwareCorrupted: %5lu kB\n"
> +        # ifdef CONFIG_CMA
> +        totalcma_pages = int(gdb.parse_and_eval("totalcma_pages"))
> +        gdb.write(
> +            "CmaTotal:       {:8d} kB\n".format(self.K(totalcma_pages)) +
> +            "CmaFree:        {:8d} kB\n".format(self.gps_K("NR_FREE_CMA_PAGES"))
> +            )
> +
> +LxMeminfo()
> 

Jan

-- 
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Corporate Competence Center Embedded Linux