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    SubjectRe: [PATCH v2] After swapout/swapin private dirty mappings are reported clean in smaps
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    On Wednesday 15 September 2010 19:44:17 Richard Guenther wrote:
    > On Wed, 15 Sep 2010, Balbir Singh wrote:
    > > * Nikanth Karthikesan <knikanth@suse.de> [2010-09-15 12:01:11]:
    > > > How? Current smaps information without this patch provides incorrect
    > > > information. Just because a private dirty page became part of swap
    > > > cache, it shown as clean and backed by a file. If it is shown as clean
    > > > and backed by swap then it is fine.
    > >
    > > How is GDB using this information?
    >
    > GDB counts the number of dirty and swapped pages in a private mapping and
    > based on that decides whether it needs to dump it to a core file or not.
    > If there are no dirty or swapped pages gdb assumes it can reconstruct
    > the mapping from the original backing file. This way for example
    > shared libraries do not end up in the core file.
    >

    Well, may be /proc/pid/pagemap + /proc/kpageflags is enough for this! One can
    get the pageflags using these interfaces. See Documentation/vm/pagemap.txt for
    the explanation on how to do it. There is also a sample program that prints
    page flags using this interface in Documentation/vm/page-types.c.

    It is bad that /proc/pid/pagemap is never mentioned in
    Documentation/filesystems/proc.txt. I will send a patch to rectify this.

    Thanks
    Nikanth


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