Updated the bug.
On Mon, Aug 1, 2011 at 8:31 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
> On Tue, 26 Jul 2011, Jojy Varghese wrote:
>> Sage
>> Attached is the dmesg outputs after an scp of three level
>> directory. Here is how the directory tree looks like:
>>
>>
>> testscpdirB/
>> ÿÿÿÿÿÿ level1
>> ÿÿÿÿÿÿ l1f1
>> ÿÿÿÿÿÿ l1f2
>> ÿÿÿÿÿÿ l1f3
>> ÿÿÿÿÿÿ level2
>> ÿÿÿÿÿÿ l2f1
>> ÿÿÿÿÿÿ l2f2
>> ÿÿÿÿÿÿ l2f3
>> ÿÿÿÿÿÿ l2f4
>> ÿÿÿÿÿÿ level3
>> ÿÿÿÿÿÿ l3f1
>>
>> "scp_c_kernel.log" has one more level of detail in the log
>> (ceph_fill_trace) and I changed the top level directory name. You will
>> observe that the top level directory has "have_lease" false.
>>
>> As you will see in the log, the top level dentry is looked up multiple times.
>
> Hmm, yep, that is strange! Looks like a bug, although it may be one we
> already fixed in the last kernel. Can you confirm which version of the
> kernel client and server side you are running?
>
> Also, can you do it one more time with everything in inode.c and caps.c
> enabled (or just the scripts/kcon_most.sh from ceph.git), and also the mds
> log (debug mds = 20, debug ms = 1)? That will have everything I need.
>
> Opened ticket #1350 to track this.
>
> Thanks!
> sage
>
>
>>
>>
>> thx,
>> Jojy
>>
>>
>>
>> On Tue, Jul 26, 2011 at 10:56 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> > On Tue, 26 Jul 2011, Jojy Varghese wrote:
>> >> Sage
>> >> I tried the simple use case of mkdir on the ceph mounted dir but
>> >> still see the issue. So i am wondering if our setup has anything to do
>> >> with it (although ideally it should not). Anything i should be looking
>> >> at given this behavior?'
>> >
>> > Can you capture the mds and kernel logs for the simple case?
>> >
>> > debug mds = 20
>> > debug ms = 1
>> >
>> > and for the kernel side run ceph.git's src/scripts/kcon_most.sh (or
>> > similar)
>> >
>> > Thanks!
>> > sage
>> >
>> >>
>> >>
>> >>
>> >> thx
>> >> Jojy
>> >>
>> >> On Mon, Jul 25, 2011 at 9:12 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> >> > On Mon, 25 Jul 2011, Jojy Varghese wrote:
>> >> >> What i observe is that after a mkdir, the inode CAPS loses the
>> >> >> lease(FILE_SHARED). I would have thought that the owing client should
>> >> >> have a FILE_EXCL on the files/dirs it creates.
>> >> >>
>> >> >> Since it doesnt have a lease, the dentry(after splicing) is not cached.
>> >> >
>> >> > Can you describe the specific sequence of operations you're doing? I'm
>> >> > not seeing this behavior. I see
>> >> >
>> >> > $ mkdir foo
>> >> > client->mds lookup #1/foo
>> >> > client->mds mkdir #1/foo
>> >> > $ mkdir foo/a
>> >> > client->mds lookup #100000000/a
>> >> > client->mds mkdir #100000000/a
>> >> >
>> >> > with no repeated lookup on foo.
>> >> >
>> >> > sage
>> >> >
>> >> >
>> >> >>
>> >> >> thanks
>> >> >> Jojy
>> >> >>
>> >> >> On Sat, Jul 23, 2011 at 2:56 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> >> >> > On Fri, 22 Jul 2011, Jojy Varghese wrote:
>> >> >> >> Not sure how it is designed to work but I assume that some kind of
>> >> >> >> async RPC mechanism exists from the MDCs to the clients to update the
>> >> >> >> CAP for a file from "exclusive" to "shared". This will allow the
>> >> >> >> cached dentries to be pruned/dropped when another client updates the
>> >> >> >> file.
>> >> >> >
>> >> >> > Right. If the MDS needs to modify a dentry, it revoke any issued client
>> >> >> > leases before granting the write/exclusive lock to process the request.
>> >> >> >
>> >> >> > sage
>> >> >> >
>> >> >> >>
>> >> >> >> -Jojy
>> >> >> >>
>> >> >> >> On Fri, Jul 22, 2011 at 8:51 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> >> >> >> > On Fri, 22 Jul 2011, Jojy Varghese wrote:
>> >> >> >> >> Sage would the latest patches fix the lookup issue?
>> >> >> >> >
>> >> >> >> > No, the blocker there is the '[PATCH] vfs: add d_prune dentry operation'
>> >> >> >> > email on Jul 8 to linux-fsdevel and lkml. Once this set goes in (and
>> >> >> >> > cleans up a bunch of stuff Al found in a code audit last weekend) I'll be
>> >> >> >> > bugging him about it again.
>> >> >> >> >
>> >> >> >> > sage
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >>
>> >> >> >> >> On Thu, Jul 21, 2011 at 10:55 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> >> >> >> >> > On Thu, 21 Jul 2011, Jojy Varghese wrote:
>> >> >> >> >> >> Thanks for the response Sage. We are using 2.6.39 kernel and in the
>> >> >> >> >> >> "ceph_lookup" method, i see that there is a shortcut for deciding
>> >> >> >> >> >> ENOENT but after the MDS lookup, i dont see a d_add. I am sure i am
>> >> >> >> >> >> missing something here.
>> >> >> >> >> >
>> >> >> >> >> > dout(" dir %p complete, -ENOENT\n", dir);
>> >> >> >> >> > d_add(dentry, NULL);
>> >> >> >> >> >
>> >> >> >> >> > ...but that is only for the negative lookup in a directory with the
>> >> >> >> >> > 'complete' flag set. And it's never set currently because we don't have
>> >> >> >> >> > d_prune yet (and the old use of d_release was racy). So ignore this part
>> >> >> >> >> > for now!
>> >> >> >> >> >
>> >> >> >> >> > You have an existing, unchanging, directory that you're seeing repeated
>> >> >> >> >> > lookups on, right? Like the top-level directory in the heirarchy you're
>> >> >> >> >> > copying? And the client is doing repeated lookups on the same name?
>> >> >> >> >> >
>> >> >> >> >> > The way to debug this is probably to start with the messages passing to
>> >> >> >> >> > the MDS and verifying that lookups are duplicated. Then enable the
>> >> >> >> >> > logging on the kernel client and see why the client isn't uses leases or
>> >> >> >> >> > the FILE_SHARED cap to avoid them. We can help you through that on #ceph
>> >> >> >> >> > if you like.
>> >> >> >> >> >
>> >> >> >> >> > sage
>> >> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> >>
>> >> >> >> >> >> thanks again
>> >> >> >> >> >> Jojy
>> >> >> >> >> >>
>> >> >> >> >> >> On Thu, Jul 21, 2011 at 9:49 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote:
>> >> >> >> >> >> > On Thu, 21 Jul 2011, Jojy Varghese wrote:
>> >> >> >> >> >> >> Hi
>> >> >> >> >> >> >> I just started looking at the ceph code in kernel and had a question
>> >> >> >> >> >> >> about performance considerations for lookup operations. I noticed that
>> >> >> >> >> >> >> for every operation (say copying a directory), the root dentry is
>> >> >> >> >> >> >> "looked" up multiple times and since they all go to MDS for the actual
>> >> >> >> >> >> >> lookup operation, it effects the performance. I am sure consistency is
>> >> >> >> >> >> >> the winner here. Is there any plan to improve this, maybe by having
>> >> >> >> >> >> >> MDS push the capability down to the clients when the dentry is
>> >> >> >> >> >> >> updated. So say from CAP_EXCL to CAP_SHARED when the dentry is
>> >> >> >> >> >> >> modified. This was the client node can cache the lookup operation and
>> >> >> >> >> >> >> does not have to make a round trip to the MDS.
>> >> >> >> >> >> >
>> >> >> >> >> >> > In general, the MDS has two ways of keeping a client's cached dentry
>> >> >> >> >> >> > consistent:
>> >> >> >> >> >> >
>> >> >> >> >> >> > - it can issue the FILE_SHARED capability bit on the parent directory,
>> >> >> >> >> >> > which means the entire directory is static and the client can cache
>> >> >> >> >> >> > dentry.
>> >> >> >> >> >> > - if it can't do that, it will issue a per-dentry lease
>> >> >> >> >> >> >
>> >> >> >> >> >> > There is an additional 'complete' bit that is used to indicate on the
>> >> >> >> >> >> > client that it has the _entire_ directory in cache. If set, it can do
>> >> >> >> >> >> > negative lookups and readdir without hitting the MDS. That's currently
>> >> >> >> >> >> > broken, pending the addition of a d_prune dentry_operation (see
>> >> >> >> >> >> > linux-fsdevel email from July 8).
>> >> >> >> >> >> >
>> >> >> >> >> >> > Anyway, long story short, if you're seeing repeated lookups on a dentry
>> >> >> >> >> >> > that isn't changing, something is broken. Can you describe the workload
>> >> >> >> >> >> > in more detail? Which versions of the client and mds are you running?
>> >> >> >> >> >> >
>> >> >> >> >> >> > sage
>> >> >> >> >> >> >
>> >> >> >> >> >> >
>> >> >> >> >> >> --
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>> >> >> >> >> >>
>> >> >> >> >> >>
>> >> >> >> >>
>> >> >> >> >>
>> >> >> >> --
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>> >> >> >>
>> >> >> >>
>> >> >>
>> >> >>
>> >> --
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>> >>
>>
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