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    SubjectRe: [PATCH] cache last free vmap_area to avoid restarting beginning
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    Date
    Hi,

    On Thu, 2010-05-06 at 02:16 +1000, Nick Piggin wrote:
    > On Wed, May 05, 2010 at 01:48:48PM +0100, Steven Whitehouse wrote:
    > > Hi,
    > >
    > > On Mon, 2010-05-03 at 02:29 +0900, Minchan Kim wrote:
    > > > Hi, Steven.
    > > >
    > > > Sorry for lazy response.
    > > > I wanted to submit the patch which implement Nick's request whole.
    > > > And unfortunately, I am so busy now.
    > > > But if it's urgent, I want to submit this one firstly and
    > > > at next version, maybe I will submit remained TODO things
    > > > after middle of May.
    > > >
    > > > I think this patch can't make regression other usages.
    > > > Nick. What do you think about?
    > > >
    > > I guess the question is whether the remaining items are essential for
    > > correct functioning of this patch, or whether they are "it would be nice
    > > if" items. I suspect that they are the latter (I'm not a VM expert, but
    > > from the brief descriptions it looks like that to me) in which case I'd
    > > suggest send the currently existing patch first and the following up
    > > with the remaining changes later.
    > >
    > > We have got a nice speed up with your current patch and so far as I'm
    > > aware not introduced any new bugs or regressions with it.
    > >
    > > Nick, does that sound ok?
    >
    > Just got around to looking at it again. I definitely agree we need to
    > fix the regression, however I'm concerned about introducing other
    > possible problems while doing that.
    >
    > The following patch should (modulo bugs, but it's somewhat tested) give
    > no difference in the allocation patterns, so won't introduce virtual
    > memory layout changes.
    >
    > Any chance you could test it?
    >

    At last some further info on the failed boot during testing. The
    messages look like this:

    dracut: Starting plymouth daemon
    G------------[ cut here ]------------
    kernel BUG at mm/vmalloc.c:391!
    invalid opcode: 0000 [#1] SMP
    last sysfs file: /sys/devices/virtual/vtconsole/vtcon0/uevent
    CPU 7
    Modules linked in:
    Pid: 193, comm: modprobe Tainted: G W 2.6.32-23.el6.bz583026.patches2.3.7.x86_64 #1 ProLiant DL580 G3
    RIP: 0010:[<ffffffff8113c161>] [<ffffffff8113c161>] alloc_vmap_area+0x431/0x440
    RSP: 0018:ffff8803dae3bcf8 EFLAGS: 00010287
    RAX: ffffc9001232e000 RBX: 0000000000004000 RCX: 0000000000000000
    RDX: ffffffffa0000000 RSI: ffff8803db66fdc0 RDI: ffffffff81b6d0a0
    RBP: ffff8803dae3bd88 R08: 000000000000000a R09: 00000000000000d0
    R10: ffff8803db6b6e40 R11: 0000000000000040 R12: 0000000000000001
    R13: ffffffffff000000 R14: ffffffffffffffff R15: ffffffffa0000000
    FS: 00007f5872189700(0000) GS:ffff88002c2e0000(0000) knlGS:0000000000000000

    and the code around that point is:

    static struct vmap_area *alloc_vmap_area(unsigned long size,
    unsigned long align,
    unsigned long vstart, unsigned long vend,
    int node, gfp_t gfp_mask)
    {

    ...

    if (!first)
    goto found;

    if (first->va_start < addr) {
    391> BUG_ON(first->va_end < addr);
    n = rb_next(&first->rb_node);
    addr = ALIGN(first->va_end + PAGE_SIZE, align);
    if (n)
    first = rb_entry(n, struct vmap_area, rb_node);
    else
    goto found;
    }


    so that seems to pinpoint the line on which the problem occurred. Let us
    know if you'd like us to do some more testing. I think we have the
    console access issue fixed now. Many thanks for all you help in this
    so far,

    Steve.






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