[lustre-devel] Request arc buffer, zerocopy

[Andreas Dilger]

Add relevant developers to CC list. 

Cheers, Andreas

> On Jun 13, 2019, at 05:54, Anna Fuchs <anna.fuchs at informatik.uni-hamburg.de> wrote:
> 
> Dear all,
> 
> in osd-zfs/osd_io.c:osd_bufs_get_write you can find a comment regarding zerocopy:
> 
> 	/*
> 	 * currently only full blocks are subject to zerocopy approach:
> 	 * so that we're sure nobody is trying to update the same block
> 	 */
> 
> Whenever a block to be written is full, an arc buffer is requested, otherwise alloc_page.
> 
> I do not really understand the conclusion. Why and how do full blocks prevent updates?
> And put it differently - why not to try zerocopy for not full blocks?
> What could happen if I tried to request an arc buffer for e.g. a block with missin g last page?
> 
> I would be greateful for details.
> Best regards
> Anna
> 
> 
> 
> 
> 
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