Could you explain why client can add page cache later? Please
correct where it is wrong.
1. Client A has page cache of file X
2. Client B open X for write, it will take write lock and MDS
will revoke Fc of Client A, which will result in Client A drop its
cache.
3. Client A try to read X, Client A can go ahead to read from
OSD, which gets the old data. (will clinet A issue a getattr to MDS?
will the getattr been blocked? I see some discussion pointing to
https://github.com/ukernel/ceph/commit/7db1563416b5559310dbbc834795b83a4ccdaab4)
4. Client B writes data
5. Client A still get old data.
-Xiaoxi
Yan, Zheng <ukernel@xxxxxxxxx> 于2020年9月24日周四 上午11:50写道：
>
> On Thu, Sep 24, 2020 at 11:07 AM Xiaoxi Chen <superdebuger@xxxxxxxxx> wrote:
> >
> > Hi zheng,
> > We are seeing inconsistent among clients ones one client update a file(by scp), some of the node see new contents but some of the nodes don't. The inconsistent can last 30mins to a few hours and fix by its own. I think it should because some of the node not dropping the page cache properly.
> > Looking into the code I see when Fc cap revoke, fuse client drop objectcache , queue a task to finisher thread to do fuse_lowlevel_notify_inval_inode, then ack the cap revoke. So seems there is a window between the cap-revoke-ack , and the final fuse_lowlevel_notify_inval_inode finished, in this window page cache still valid and user can read stale data. Though it is strange that the window can be that large(no pg issue during the window).
> > Could you please confirm if this is the real problems and why it is implemented in this way?
> >
>
> yes, it's real problem. fuse_lowlevel_notify_inval_inode() does not
> prevent client add page cache later. If there are multiple fuse
> clients read/modify same file, you'd better to set
> fuse_disable_pagecache option to true.
>
> > -xiaoxi
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