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    SubjectRe: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory pressure: box ==> doorstop
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    On Tue, 2008-01-08 at 16:27 +0100, Mike Galbraith wrote:
    > On Tue, 2008-01-08 at 16:21 +0100, Mike Galbraith wrote:
    > > On Tue, 2008-01-08 at 03:38 -0800, Andrew Morton wrote:
    > > >
    > > > Well. From your earlier trace it appeared that something was causing
    > > > the filesystem to perform synchronous inode writes - sync_dirty_buffer() was
    > > > called.
    > > >
    > > > This will cause many more seeks than would occur if we were doing full
    > > > delayed writing, with obvious throughput implications.
    > >
    > > Yes, with UDF, the IO was _incredibly_ slow. With ext2, it was better,
    > > though still very bad. I tested with that other OS, and it gets ~same
    > > throughput with UDF as I got with ext2 (ick).
    > >
    > > UDF does udf_clear_inode() -> write_inode_now(inode, 1)
    > >
    > > I suppose I could try write_inode_now(inode, 0). Might unstick the box.
    >
    > (nope, still sync, UDF still deadly)

    write_inode_now() is a fibber.

    The below seems to fix it in that writes dribbling to the DVD+RW at the
    whopping 1 to 10 pages/sec I'm seeing no longer turn box into a
    doorstop. It's probably busted as heck.

    Think I'll cc linux-mm, and go find something safer to play with.

    diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    index 0fca820..f1cce24 100644
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -657,7 +657,7 @@ int write_inode_now(struct inode *inode, int sync)
    int ret;
    struct writeback_control wbc = {
    .nr_to_write = LONG_MAX,
    - .sync_mode = WB_SYNC_ALL,
    + .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
    .range_start = 0,
    .range_end = LLONG_MAX,
    };
    diff --git a/fs/udf/inode.c b/fs/udf/inode.c
    index 6ff8151..d1fc116 100644
    --- a/fs/udf/inode.c
    +++ b/fs/udf/inode.c
    @@ -117,7 +117,7 @@ void udf_clear_inode(struct inode *inode)
    udf_discard_prealloc(inode);
    udf_truncate_tail_extent(inode);
    unlock_kernel();
    - write_inode_now(inode, 1);
    + write_inode_now(inode, 0);
    }
    kfree(UDF_I_DATA(inode));
    UDF_I_DATA(inode) = NULL;



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