Squashed commit of the following:

commit 988a326fa22d6fabda04b5ec7a36fcc1b58a6bb2
Author: Lee Susman <lsusman@codeaurora.org>
Date:   Sun May 5 17:31:17 2013 +0300

    mm: pass readahead info down to the i/o scheduler

    Some i/o schedulers (i.e. row-iosched, cfq-iosched) deploy an idling
    algorithm in order to be better synced with the readahead algorithm.
    Idling is a prediction algorithm for incoming read requests.

    In this patch we mark pages which are part of a readahead window, by
    setting a newly introduced flag. With this flag, the i/o scheduler can
    identify a request which is associated with a readahead page. This
    enables the i/o scheduler's idling mechanism to be en-sync with the
    readahead mechanism and, in turn, can increase read throughput.

    Change-Id: I0654f23315b6d19d71bcc9cc029c6b281a44b196
    Signed-off-by: Lee Susman <lsusman@codeaurora.org>

commit 6e42d2a595838d1eb12c24e4cf1675e341f98eb1
Author: Tatyana Brokhman <tlinder@codeaurora.org>
Date:   Thu Jul 25 13:45:21 2013 +0300

    block: row: Remove warning massage from add_request

    Regular priority queues is marked as "starved" if it skipped a dispatch
    due to being empty. When a new request is added to a "starved" queue
    it will be marked as urgent.
    The removed WARN_ON was warning about an impossible case when a regular
    priority (read) queue was marked as starved but wasn't empty. This is
    a possible case due to the bellow:
    If the device driver fetched a read request that is pending for
    transmission and an URGENT request arrives, the fetched read will be
    reinserted back to the scheduler. Its possible that the queue it will be
    reinserted to was marked as "starved" in the meanwhile due to being empty.

    CRs-fixed: 517800
    Change-Id: Iaae642ea0ed9c817c41745b0e8ae2217cc684f0c
    Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

commit 91ab76debc19a1fe5290369c4b4886dbb54ecbbc
Author: Tatyana Brokhman <tlinder@codeaurora.org>
Date:   Sun Jul 7 17:33:05 2013 +0300

    block: Add URGENT request notification support to CFQ scheduler

    When the scheduler reports to the block layer that there is an urgent
    request pending, the device driver may decide to stop the transmission
    of the current request in order to handle the urgent one. This is done
    in order to reduce the latency of an urgent request. For example:
    long WRITE may be stopped to handle an urgent READ.

    Change-Id: I3072b8a1423870fed9c04c28d93caaf9557a7b89
    Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

commit be557c3f9b8944509293955da9be62bb292787e6
Author: Tatyana Brokhman <tlinder@codeaurora.org>
Date:   Tue Jul 2 14:43:13 2013 +0300

    block: row: change hrtimer_cancel to hrtimer_try_to_cancel

    Calling hrtimer_cancel with interrupts disabled can result in a livelock.
    When flushing plug list in the block layer interrupts are disabled and an
    hrtimer is used when adding requests from that plug list to the scheduler.
    In this code flow, if the hrtimer (which is used for idling) is set, it's
    being canceled by calling hrtimer_cancel. hrtimer_cancel will perform
    the following in an endless loop:
    1. try cancel the timer
    2. if fails - rest_cpu
    the cancellation can fail if the timer function already started. Since
    interrupts are disabled it can never complete.
    This patch reduced the number of times the hrtimer lock is taken while
    interrupts are disabled by calling hrtimer_try_co_cancel. the later will
    try to cancel the timer just once and return with an error code if fails.

    CRs-fixed: 499887
    Change-Id: I25f79c357426d72ad67c261ce7cb503ae97dc7b9
    Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

commit e33e599a5527e24d2a41252937d625dac4e86cdb
Author: Lee Susman <lsusman@codeaurora.org>
Date:   Sun Jun 23 16:27:40 2013 +0300

    block: row-iosched idling triggered by readahead pages

    In the current implementation idling is triggered only by request
    insertion frequency. This heuristic is not very accurate and may hit
    random requests that shouldn't trigger idling. This patch uses the
    PG_readahead flag in struct page's flags, which indicates that the page
    is part of a readahead window, to start idling upon dispatch of a request
    associated with a readahead page.

    The above readehead flag is used together with the existing
    insertion-frequency trigger. The frequency timer will catch read requests
    which are not part of a readahead window, but are still part of a
    sequential stream (and therefore dispatched in small time intervals).

    Change-Id: Icb7145199c007408de3f267645ccb842e051fd00
    Signed-off-by: Lee Susman <lsusman@codeaurora.org>

commit fa709c01d23bcb5afe4651bca751327b5f4e22f0
Author: Tatyana Brokhman <tlinder@codeaurora.org>
Date:   Thu May 16 14:36:58 2013 +0300

    block: Remove "requeuing urgent req" error messages

    It is possible for URGENT request to be requeued/reinserted if it was
    fetched during the creation of a packed list. This end case is rare and is
    not handled at the moment.
    This patch changes the messages notifying of the above to debug level
    (instead of error) in order to clear the dmesg log.

    Change-Id: Ie8bc067e61559a6f702077b95c5dbcc426404232
    Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>