Sage,
Will get back to you with the logs.
Had another question about the implementation:
Here is the piece of code that I am a bit confused about:
In "fs/ceph/inode.c" ( function "ceph_fill_trace")
/* do we have a lease on the whole dir? */
have_dir_cap =
(le32_to_cpu(rinfo->diri.in->cap.caps) &
CEPH_CAP_FILE_SHARED);
/* do we have a dn lease? */
have_lease = have_dir_cap ||
(le16_to_cpu(rinfo->dlease->mask) &
CEPH_LOCK_DN);
So we check the capability "CEPH_CAP_FILE_SHARED" to make sure the
entire directory has the lease. "have_lease" is then used to
determine if the dentry can be cached.
I would have thought that it should be "CEPH_CAP_FILE_EXCL" that
should be used to determine if a dentry can be cached since it would
mean that the client created the file and has "update" capabilities.
thanks
-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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