[Linux-cachefs] [PATCH] ceph: Update the pages in fscache in writepages() path
Yan, Zheng
ukernel at gmail.com
Wed Nov 20 01:18:31 UTC 2013
On Wed, Nov 20, 2013 at 12:05 AM, Milosz Tanski <milosz at adfin.com> wrote:
> Yan and Sage,
>
> I've ran into this issue again on my test cluster. The client hangs
> all requests for a particular inode, I did a dump cache to see what's
> going... but I don't understand to enough to be able to read this line
> well enough.
>
> Can you guys help me read this, so I can further track down and
> hopefully fix this issue.
>
> [inode 10000346eed [2,head]
> /petabucket/beta/17511b3d12466609785b6a0e34597431721d177240371c0a1a4e347a1605381b/advertiser_id.dict
> auth v214 ap=5+0 dirtyparent s=925 n(v0 b925 1=1+0) (ifile sync->mix)
> (iversion lock) cr={59947=0-4194304 at 1}
> caps={59947=pAsLsXsFr/pAsxXsxFxwb at 26,60001=pAsLsXsFr/- at 1,60655=pAsLsXsFr/pAsLsXsFscr/pFscr at 36}
> | ptrwaiter=0 request=4 lock=1 caps=1 dirtyparent=1 dirty=1 waiter=1
> authpin=1 0x17dd6b70]
>
> root at bnode-16a1ed7d:~# cat
> /sys/kernel/debug/ceph/e23a1bfc-8328-46bf-bc59-1209df3f5434.client60655/mdsc
> 15659 mds0 getattr #10000346eed
> 15679 mds0 getattr #10000346eed
> 15710 mds0 getattr #10000346eed
> 15922 mds0 getattr #10000346eed
which kernel do you use? is there any blocked process (echo w >
/proc/sysrq-trigger) on client.60655 ? 3.12 kernel contains few fixes
for similar hang.
Regards
Yan, Zheng
>
> On Wed, Nov 6, 2013 at 10:01 AM, Yan, Zheng <ukernel at gmail.com> wrote:
>> On Wed, Nov 6, 2013 at 9:41 PM, Milosz Tanski <milosz at adfin.com> wrote:
>>> Sage,
>>>
>>> I think the incrementing version counter on the whole is a neater
>>> solution then using size and mtime. If nothing else it's more explicit
>>> in the the read cache version. With what you suggested plus additional
>>> changes to the open code (where the cookie gets created) the
>>> write-through scenario should be correct.
>>>
>>> Sadly, my understanding of the MDS protocol is still not great. So
>>> when doing this in the first place I erred on the side of using what
>>> was already in place.
>>>
>>> In a kind of un-related question. Is there a debug hook in the kclient
>>> (or MDS for that matter) to dump the current file inodes (names) with
>>> issues caps and to which hosts. This would be very helpful for
>>> debugging, since from time to time I see a one of the clients get
>>> stuck in getattr (via mdsc debug log).
>>>
>>
>> "ceph mds tell \* dumpcache" dump the mds cache to a file. the dump
>> file contains caps information.
>>
>> Regards
>> Yan, Zheng
>>
>>> Thanks,
>>> - Milosz
>>>
>>> On Tue, Nov 5, 2013 at 6:56 PM, Sage Weil <sage at inktank.com> wrote:
>>>> On Tue, 5 Nov 2013, Milosz Tanski wrote:
>>>>> Li,
>>>>>
>>>>> First, sorry for the late reply on this.
>>>>>
>>>>> Currently fscache is only supported for files that are open in read
>>>>> only mode. I originally was going to let fscache cache in the write
>>>>> path as well as long as the file was open in with O_LAZY. I abandoned
>>>>> that idea. When a user opens the file in O_LAZY we can cache things
>>>>> locally with the assumption that the user will care of the
>>>>> synchronization in some other manner. There is no way of invalidating
>>>>> a subset of the pages in object cached by fscache, there is no way we
>>>>> can make O_LAZY work well.
>>>>>
>>>>> The ceph_readpage_to_fscache() in writepage has no effect and it
>>>>> should be removed. ceph_readpage_to_fscache() calls cache_valid() to
>>>>> see if it should perform the page save, and since the file can't have
>>>>> a CACHE cap at the point in time it doesn't do it.
>>>>
>>>> (Hmm, Dusting off my understanding of fscache and reading
>>>> fs/ceph/cache.c; watch out!) It looks like cache_valid is
>>>>
>>>> static inline int cache_valid(struct ceph_inode_info *ci)
>>>> {
>>>> return ((ceph_caps_issued(ci) & CEPH_CAP_FILE_CACHE) &&
>>>> (ci->i_fscache_gen == ci->i_rdcache_gen));
>>>> }
>>>>
>>>> and in the FILE_EXCL case, the MDS will issue CACHE|BUFFER caps. But I
>>>> think the aux key (size+mtime) will prevent any use of the cache as soon
>>>> as the first write happens and mtime changes, right?
>>>>
>>>> I think that in order to make this work, we need to fix/create a
>>>> file_version (or something similar) field in the (mds) inode_t to have
>>>> some useful value. I.e., increment it any time
>>>>
>>>> - a different client/writer comes along
>>>> - a file is modified by the mds (e.g., truncated or recovered)
>>>>
>>>> but allow it to otherwise remain the same as long as only a single client
>>>> is working with the file exclusively. This will be more precise than the
>>>> (size, mtime) check that is currently used, and would remain valid when a
>>>> single client opens the same file for exclusive read/write multiple times
>>>> but there are no other intervening changes.
>>>>
>>>> Milosz, if that were in place, is there any reason not to wire up
>>>> writepage and allow the fscache to be used write-through?
>>>>
>>>> sage
>>>>
>>>>
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> - Milosz
>>>>>
>>>>> On Thu, Oct 31, 2013 at 11:56 PM, Li Wang <liwang at ubuntukylin.com> wrote:
>>>>> > Currently, the pages in fscache only are updated in writepage() path,
>>>>> > add the process in writepages().
>>>>> >
>>>>> > Signed-off-by: Min Chen <minchen at ubuntukylin.com>
>>>>> > Signed-off-by: Li Wang <liwang at ubuntukylin.com>
>>>>> > Signed-off-by: Yunchuan Wen <yunchuanwen at ubuntukylin.com>
>>>>> > ---
>>>>> > fs/ceph/addr.c | 8 +++++---
>>>>> > 1 file changed, 5 insertions(+), 3 deletions(-)
>>>>> >
>>>>> > diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
>>>>> > index 6df8bd4..cc57911 100644
>>>>> > --- a/fs/ceph/addr.c
>>>>> > +++ b/fs/ceph/addr.c
>>>>> > @@ -746,7 +746,7 @@ retry:
>>>>> >
>>>>> > while (!done && index <= end) {
>>>>> > int num_ops = do_sync ? 2 : 1;
>>>>> > - unsigned i;
>>>>> > + unsigned i, j;
>>>>> > int first;
>>>>> > pgoff_t next;
>>>>> > int pvec_pages, locked_pages;
>>>>> > @@ -894,7 +894,6 @@ get_more_pages:
>>>>> > if (!locked_pages)
>>>>> > goto release_pvec_pages;
>>>>> > if (i) {
>>>>> > - int j;
>>>>> > BUG_ON(!locked_pages || first < 0);
>>>>> >
>>>>> > if (pvec_pages && i == pvec_pages &&
>>>>> > @@ -924,7 +923,10 @@ get_more_pages:
>>>>> >
>>>>> > osd_req_op_extent_osd_data_pages(req, 0, pages, len, 0,
>>>>> > !!pool, false);
>>>>> > -
>>>>> > + for(j = 0; j < locked_pages; j++) {
>>>>> > + struct page *page = pages[j];
>>>>> > + ceph_readpage_to_fscache(inode, page);
>>>>> > + }
>>>>> > pages = NULL; /* request message now owns the pages array */
>>>>> > pool = NULL;
>>>>> >
>>>>> > --
>>>>> > 1.7.9.5
>>>>> >
>>>>> > --
>>>>> > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
>>>>> > the body of a message to majordomo at vger.kernel.org
>>>>> > More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Milosz Tanski
>>>>> CTO
>>>>> 10 East 53rd Street, 37th floor
>>>>> New York, NY 10022
>>>>>
>>>>> p: 646-253-9055
>>>>> e: milosz at adfin.com
>>>>>
>>>>>
>>>
>>>
>>>
>>> --
>>> Milosz Tanski
>>> CTO
>>> 10 East 53rd Street, 37th floor
>>> New York, NY 10022
>>>
>>> p: 646-253-9055
>>> e: milosz at adfin.com
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>> the body of a message to majordomo at vger.kernel.org
>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>> Please read the FAQ at http://www.tux.org/lkml/
>
>
>
> --
> Milosz Tanski
> CTO
> 10 East 53rd Street, 37th floor
> New York, NY 10022
>
> p: 646-253-9055
> e: milosz at adfin.com
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