linux-kernel - Re: [PATCH for-next v8 3/6] RDMA/rxe: Add page invalidation support

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Message-ID:
 <OS3PR01MB9865AAD73DAD668A0918E909E53D2@OS3PR01MB9865.jpnprd01.prod.outlook.com>
Date: Tue, 10 Dec 2024 12:12:47 +0000
From: "Daisuke Matsuda (Fujitsu)" <matsuda-daisuke@...itsu.com>
To: 'Jason Gunthorpe' <jgg@...dia.com>
CC: "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"leon@...nel.org" <leon@...nel.org>, "zyjzyj2000@...il.com"
	<zyjzyj2000@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "rpearsonhpe@...il.com"
	<rpearsonhpe@...il.com>, "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Subject: Re: [PATCH for-next v8 3/6] RDMA/rxe: Add page invalidation support

On Tue, Dec 10, 2024 4:31 AM Jason Gunthorpe wrote:
> On Wed, Oct 09, 2024 at 10:59:00AM +0900, Daisuke Matsuda wrote:
> 
> > +static bool rxe_ib_invalidate_range(struct mmu_interval_notifier *mni,
> > +				    const struct mmu_notifier_range *range,
> > +				    unsigned long cur_seq)
> > +{
> > +	struct ib_umem_odp *umem_odp =
> > +		container_of(mni, struct ib_umem_odp, notifier);
> > +	struct rxe_mr *mr = umem_odp->private;
> > +	unsigned long start, end;
> > +
> > +	if (!mmu_notifier_range_blockable(range))
> > +		return false;
> > +
> > +	mutex_lock(&umem_odp->umem_mutex);
> > +	mmu_interval_set_seq(mni, cur_seq);
> > +
> > +	start = max_t(u64, ib_umem_start(umem_odp), range->start);
> > +	end = min_t(u64, ib_umem_end(umem_odp), range->end);
> > +
> > +	rxe_mr_unset_xarray(mr, start, end);
> > +
> > +	/* update umem_odp->dma_list */
> > +	ib_umem_odp_unmap_dma_pages(umem_odp, start, end);
> 
> This seems like a strange thing to do, rxe has the xarray so why does
> it use the odp->dma_list?

I tried to reuse existing rxe codes for RDMA operations, and that required
to update the xarray also for ODP cases. I think using pfn_list only is technically
feasible.
> 
> I think what you want is to have rxe disable the odp->dma_list and use
> its xarray instead
> 
> Or use the odp lists as-is and don't include the xarray?

As you pointed out in reply to the next patch, the current implementation introduces
redundant copying overhead. We cannot avoid that with xarray, so I would rather
use the odp lists only.

Regards,
Daisuke

> 
> Jason