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    SubjectRe: new Areca driver in 2.6.16-rc6-mm2 appears to be broken
    Date
    Dear Jens Axboe,

    I had found a big difference of generic_make_request(struct bio *bio)
    got message : sdb1: rw=0, want=...., limit=.....


    *****************
    ** TEST 1
    *****************

    I used "MAX_XFER_SECTORS 4096" driver to do mkfs.ext2 with ARECA RAID
    volume sdb1.
    and copy a big file (900MB) into sdb1.
    If I copy this file from sdb1, the message rw=.... ,want=......,
    limit=...... will appear immediately.

    When I reboot the system and used "MAX_XFER_SECTORS 512" driver.
    I copy this big file from sdb1, the message rw=.... ,want=......,
    limit=...... still appear immediately.

    When I redo mkfs.ext2 with ARECA RAID volume sdb1 (used "MAX_XFER_SECTORS
    512")
    and copy the same file (900MB) into sdb1.
    I copy this file from sdb1 again,the message rw=.... ,want=......,
    limit=...... disappear.

    ****************
    ** TEST 2
    ****************

    When I do another test with "MAX_XFER_SECTORS 4096" driver

    #echo 0 > /sys/block/sdb/queue/read_ahead_kb
    #mkfs.ext2 /dev/sdb1

    then copy the same file (900MB) into sdb1.
    I copy this file from sdb1 again,the message rw=.... ,want=......,
    limit=...... disappear.
    Even I redo "echo 4096 > /sys/block/sdb/queue/read_ahead_kb" with ARECA RAID
    volume.
    The message rw=.... ,want=......, limit=...... never appear at my "copy
    compare" test script.

    Now I can say the bug come from "block read ahead".

    And this bug will certainly appear when do "mkfs.ext2" if read_ahead_kb
    value large enough.


    Best Regards
    Erich Chen
    ----- Original Message -----
    From: "Jens Axboe" <axboe@suse.de>
    To: "Andrew Morton" <akpm@osdl.org>
    Cc: "James Bottomley" <James.Bottomley@steeleye.com>; <erich@areca.com.tw>
    Sent: Friday, March 31, 2006 3:42 PM
    Subject: Re: new Areca driver in 2.6.16-rc6-mm2 appears to be broken


    >
    > (irk, Erich wasn't in the cc, sorry to Andrew and James for getting this
    > mail twice)
    >
    > On Thu, Mar 30 2006, Andrew Morton wrote:
    >> "erich" <erich@areca.com.tw> wrote:
    >> >
    >> > Dear Chris Caputo,
    >> >
    >> > Thanks you to conform this issue again, my colleague assisted me and
    >> > to
    >> > double check my older version driver yesterday.
    >> > and the old driver is working fine as your mention before.
    >> >
    >> > The ARCMSR_MAX_XFER_SECTORS is the reason why cause "attempt to access
    >> > beyond end of device".
    >> >
    >> > #define ARCMSR_MAX_XFER_SECTORS
    >> > 256 -----old
    >> > #define ARCMSR_MAX_XFER_SECTORS
    >> > 4096 -----new
    >>
    >> That seems odd. ARCMSR_MAX_XFER_SECTORS just gets put into
    >> scsi_host_template.max_sectors. Could it be a scsi core buglet?
    >
    > Perhaps the larger max sectors setting is causing read-ahead to be
    > overly optimistic and going beyond the end? Should not happen.
    >
    > Erich, can you try and shrink read-ahead on that device and retest?
    > Basically just do
    >
    > # echo 0 > /sys/block/sdX/queue/read_ahead_kb
    >
    > and see if it still complains.
    >
    > --
    > Jens Axboe
    >

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