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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Gal Pressman <galpress@amazon.com>
Cc: Michal Kalderon <michal.kalderon@marvell.com>,
	mkalderon@marvell.com, aelior@marvell.com, dledford@redhat.com,
	bmt@zurich.ibm.com, sleybo@amazon.com, leon@kernel.org,
	linux-rdma@vger.kernel.org
Subject: Re: [PATCH v11 rdma-next 6/7] RDMA/qedr: Add doorbell overflow recovery support
Date: Fri, 20 Sep 2019 10:38:17 -0300
Message-ID: <20190920133817.GB7095@ziepe.ca> (raw)
In-Reply-To: <a0e19fb2-cd5c-4394-16d6-75ac856340b4@amazon.com>

On Fri, Sep 20, 2019 at 04:30:52PM +0300, Gal Pressman wrote:
> On 19/09/2019 21:02, Jason Gunthorpe wrote:
> > On Thu, Sep 05, 2019 at 01:01:16PM +0300, Michal Kalderon wrote:
> > 
> >> @@ -347,6 +360,9 @@ void qedr_mmap_free(struct rdma_user_mmap_entry *rdma_entry)
> >>  {
> >>  	struct qedr_user_mmap_entry *entry = get_qedr_mmap_entry(rdma_entry);
> >>  
> >> +	if (entry->mmap_flag == QEDR_USER_MMAP_PHYS_PAGE)
> >> +		free_page((unsigned long)phys_to_virt(entry->address));
> >> +
> > 
> > While it isn't wrong it do it this way, we don't need this mmap_free()
> > stuff for normal CPU pages. Those are refcounted and qedr can simply
> > call free_page() during the teardown of the uobject that is using the
> > this page. This is what other drivers already do.
> 
> This is pretty much what EFA does as well.  When we allocate pages
> for the user (CQ for example), we DMA map them and later on mmap
> them to the user. We expect those pages to remain until the entry is
> freed, how can we call free_page, who is holding a refcount on those
> except for the driver?

free_page is kind of a lie, it is more like put_page (see
__free_pages). I think the difference is that it assumes the page came
from alloc_page and skips some generic stuff when freeing it.

When the driver does vm_insert_page the vma holds another refcount and
the refcount does not go to zero until that page drops out of the
vma (ie at the same time mmap_free above is called). 

Then __put_page will do the free_unref_page(), etc.

So for CPU pages it is fine to not use mmap_free so long as
vm_insert_page is used

Jason

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05 10:01 [PATCH v11 rdma-next 0/7] RDMA/qedr: Use the doorbell overflow recovery mechanism for RDMA Michal Kalderon
2019-09-05 10:01 ` [PATCH v11 rdma-next 1/7] RDMA/core: Move core content from ib_uverbs to ib_core Michal Kalderon
2019-09-05 10:01 ` [PATCH v11 rdma-next 2/7] RDMA/core: Create mmap database and cookie helper functions Michal Kalderon
2019-09-19 17:14   ` Jason Gunthorpe
2019-09-19 17:48   ` Jason Gunthorpe
2019-09-19 18:07   ` Jason Gunthorpe
2019-09-23  9:36     ` [EXT] " Michal Kalderon
2019-09-23 13:30       ` Jason Gunthorpe
2019-09-24  8:31         ` Michal Kalderon
2019-09-24 12:37           ` Jason Gunthorpe
2019-09-05 10:01 ` [PATCH v11 rdma-next 3/7] RDMA/efa: Use the common mmap_xa helpers Michal Kalderon
2019-09-19 17:37   ` Jason Gunthorpe
2019-09-23  9:15     ` Michal Kalderon
2019-09-23 13:28       ` Jason Gunthorpe
2019-09-05 10:01 ` [PATCH v11 rdma-next 4/7] RDMA/siw: " Michal Kalderon
2019-09-05 10:01 ` [PATCH v11 rdma-next 5/7] RDMA/qedr: Use the common mmap API Michal Kalderon
2019-09-19 17:55   ` Jason Gunthorpe
2019-09-20 13:39     ` Gal Pressman
2019-09-23  9:21       ` Michal Kalderon
2019-09-23 13:29         ` Jason Gunthorpe
2019-09-24  8:25           ` [EXT] " Michal Kalderon
2019-09-24  8:49         ` Pressman, Gal
2019-09-24  9:31           ` Michal Kalderon
2019-10-20  7:19             ` Gal Pressman
2019-10-21 17:33               ` Jason Gunthorpe
2019-10-23  6:40                 ` Gal Pressman
2019-10-23 14:41                   ` Jason Gunthorpe
2019-10-24  8:06                     ` Gal Pressman
2019-09-05 10:01 ` [PATCH v11 rdma-next 6/7] RDMA/qedr: Add doorbell overflow recovery support Michal Kalderon
2019-09-19 18:02   ` Jason Gunthorpe
2019-09-20 13:30     ` Gal Pressman
2019-09-20 13:38       ` Jason Gunthorpe [this message]
2019-09-20 14:00         ` Gal Pressman
2019-09-23  9:37           ` Michal Kalderon
2019-09-25 19:16         ` [EXT] " Michal Kalderon
2019-09-25 19:21           ` Jason Gunthorpe
2019-09-25 19:37             ` Michal Kalderon
2019-09-26 19:10               ` Jason Gunthorpe
2019-09-23  9:30     ` Michal Kalderon
2019-09-23 13:26       ` Jason Gunthorpe
2019-09-05 10:01 ` [PATCH v11 rdma-next 7/7] RDMA/qedr: Add iWARP doorbell " Michal Kalderon

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