> On Jul 27, 2016, at 08:15, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote:
>
>
>> On Jul 27, 2016, at 07:55, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>>
>> After adding more debugging, I see that all of that is working correctly,
>> but the first LAYOUTCOMMIT is taking the size back down to 4096 from the
>> last nfs_writeback_done(), and the second LAYOUTCOMMIT never brings it back
>> up again.
>>
>
> Excellent! Thanks for debugging that.
>
>> Now I see that we should be marking the block extents as written atomically with
>> setting LAYOUTCOMMIT and nfsi->layout->plh_lwb, otherwise a LAYOUTCOMMIT can
>> collect extents just added from the next bl_write_cleanup(). Then, the next
>> LAYOUTCOMMIT fails, and all we're left with is the size from the first
>> LAYOUTCOMMIT. Not sure if that particular problem is the whole fix, but
>> that's something to work on.
>>
>> I see ways to fix that:
>>
>> - make a new pnfs_set_layoutcommit_locked() that can be used to call
>> ext_tree_mark_written() inside the i_lock
>>
>> - make another pnfs_layoutdriver_type operation to be used within
>> pnfs_set_layoutcommit (mark_layoutcommit? set_layoutcommit?), and call
>> ext_tree_mark_written() within that..
>>
>> - have .prepare_layoutcommit return a new positive plh_lwb that would
>> extend the current LAYOUTCOMMIT
>>
>> - make ext_tree_prepare_commit only encode up to plh_lwb
>
> I see no reason why ext_tree_prepare_commit() shouldn’t be allowed to extend the args->lastbytewritten. This is a metadata operation that is owned by the pNFS layout driver.
> The only thing I’d note is you should then rewrite the failure case in pnfs_layoutcommit_inode() so that it doesn’t rely on the saved “end_pos”, but uses args->lastbytewritten instead (with a comment to the effect why)…
In fact, given the potential for races here, I think the right thing to do is to have ext_tree_prepare_commit() always set the correct value for args->lastbytewritten.
Cheers
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