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    SubjectRe: [patch 8/9] LTTng instrumentation - filemap

    * Mathieu Desnoyers <> wrote:

    > Index: linux-2.6-lttng/mm/filemap.c

    > +DEFINE_TRACE(wait_on_page_start);
    > +DEFINE_TRACE(wait_on_page_end);

    These are extremely incomplete - to the level of being useless.

    To understand the lifetime of the pagecache, the following basic
    events have to be observed and instrumented:

    - create a new page
    - fill in a new page
    - dirty a page [when we know this]
    - request writeout of a page
    - clean a page / complete writeout
    - free a page due to MM pressure
    - free a page due to truncation/delete

    The following additional events are useful as well:

    - mmap a page to a user-space address
    - copy a page to a user-space address (read)
    - write to a page from a user-space address (write)
    - unmap a page from a user-space address
    - fault in a user-space mapped pagecache page

    - shmem attach/detach events
    - shmem map/unmap events
    - hugetlb map/unmap events

    I'm sure i havent listed them all. Have a look at the function-graph
    tracer output to see what kind of basic events can happen to a
    pagecache page.


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