linux-kernel - Re: [patch 1/2] block, drbd: fix drbd_req

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Date:	Sat, 7 Mar 2015 16:53:20 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Jens Axboe <axboe@...com>
cc:	Lars Ellenberg <drbd-dev@...ts.linbit.com>,
	linux-kernel@...r.kernel.org, drbd-user@...ts.linbit.com
Subject: Re: [patch 1/2] block, drbd: fix drbd_req_new() initialization

On Sat, 7 Mar 2015, Jens Axboe wrote:

> > mempool_alloc() does not support __GFP_ZERO since elements may come from
> > memory that has already been released by mempool_free().
> > 
> > Remove __GFP_ZERO from mempool_alloc() in drbd_req_new() and properly
> > initialize it to 0.
> 
> You should add it to mempool instead, avoid having this issue show up for
> other folks as well. It'd be trivial to do. Normal ->alloc() should honor
> __GFP_ZERO, just do the same manually for removing an item from the internal
> pool.
> 

Umm, it's not trivial to do and wouldn't make sense to do it.  Mempools 
don't know the element size, in other words it wouldn't know the length to 
memset() to 0 for mempool_alloc().  It shouldn't be modified to know the 
element size since elements are allocated by the implementation of 
mempool_alloc_t and they could easily become inconsistent.  This patch is 
what you want to merge, really.
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