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From: Gal Pressman <galpress@amazon.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Doug Ledford <dledford@redhat.com>, <linux-rdma@vger.kernel.org>,
	Alexander Matushevsky <matua@amazon.com>,
	Firas JahJah <firasj@amazon.com>,
	Yossi Leybovich <sleybo@amazon.com>
Subject: Re: [PATCH for-next 6/6] RDMA/efa: Do not delay freeing of DMA pages
Date: Thu, 16 Jan 2020 10:26:12 +0200
Message-ID: <2d4750ff-96ee-557d-3e52-1138dd7bebb8@amazon.com> (raw)
In-Reply-To: <20200115195104.GA929@ziepe.ca>

On 15/01/2020 21:51, Jason Gunthorpe wrote:
> On Tue, Jan 14, 2020 at 10:57:06AM +0200, Gal Pressman wrote:
>> When destroying a DMA mmapped object, there is no need to delay the
>> pages freeing to dealloc_ucontext as the kernel itself will keep
>> reference count for these pages.
> 
> Why does the commit message talk about dealloc_ucontext but doesn't
> change dealloc_ucontext?

The commit message is wrong :\, we should not delay the free_pages_exact to the
mmap_free callback. We can "put" them on destroy flow and the pages will be
freed by the last consumer (either unmap or destroy).

> 
>> +	free_pages_exact(cq->cpu_addr, cq->size);
>> 	rdma_user_mmap_entry_remove(cq->mmap_entry);
> 
> This is out of order, the pages can't be freed until the entry is
> removed.

Right, I think the order is correct except rdma_user_mmap_entry_remove should be
moved to the beginning of the function.

> 
> There is also a bug in rdma_user_mmap_entry_remove(),
> entry->driver_removed needs to be set while holding the xa_lock or
> this is not the required fence.

I see you sent a patch, I'll take a look.
Thanks for the review.

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14  8:57 [PATCH for-next 0/6] EFA updates 2020-01-14 Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 1/6] RDMA/efa: Unified getters/setters for device structs bitmask access Gal Pressman
2020-01-15 19:31   ` Jason Gunthorpe
2020-01-16  7:05     ` Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 2/6] RDMA/efa: Properly document the interrupt mask register Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 3/6] RDMA/efa: Device definitions documentation updates Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 4/6] RDMA/efa: Remove {} brackets from single statement if Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 5/6] RDMA/efa: Remove unused ucontext parameter from efa_qp_user_mmap_entries_remove Gal Pressman
2020-01-14  8:57 ` [PATCH for-next 6/6] RDMA/efa: Do not delay freeing of DMA pages Gal Pressman
2020-01-15 19:51   ` Jason Gunthorpe
2020-01-16  8:26     ` Gal Pressman [this message]
2020-01-15 19:58 ` [PATCH for-next 0/6] EFA updates 2020-01-14 Jason Gunthorpe

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