Re: [PATCH v2] IB: rework memlock limit handling code

[Leon Romanovsky <leon@kernel.org>]

On Tue, Oct 31, 2023 at 01:30:27PM +0000, Maxim Samoylov wrote:
> On 23/10/2023 07:52, Leon Romanovsky wrote:
> > On Mon, Oct 23, 2023 at 09:40:16AM +0800, Guoqing Jiang wrote:
> >>
> >>
> >> On 10/15/23 17:19, Leon Romanovsky wrote:
> >>> On Thu, Oct 12, 2023 at 01:29:21AM -0700, Maxim Samoylov wrote:
> >>>> This patch provides the uniform handling for RLIM_INFINITY value
> >>>> across the infiniband/rdma subsystem.
> >>>>
> >>>> Currently in some cases the infinity constant is treated
> >>>> as an actual limit value, which could be misleading.
> >>>>
> >>>> Let's also provide the single helper to check against process
> >>>> MEMLOCK limit while registering user memory region mappings.
> >>>>
> >>>> Signed-off-by: Maxim Samoylov<max7255@meta.com>
> >>>> ---
> >>>>
> >>>> v1 -> v2: rewritten commit message, rebased on recent upstream
> >>>>
> >>>>    drivers/infiniband/core/umem.c             |  7 ++-----
> >>>>    drivers/infiniband/hw/qib/qib_user_pages.c |  7 +++----
> >>>>    drivers/infiniband/hw/usnic/usnic_uiom.c   |  6 ++----
> >>>>    drivers/infiniband/sw/siw/siw_mem.c        |  6 +++---
> >>>>    drivers/infiniband/sw/siw/siw_verbs.c      | 23 ++++++++++------------
> >>>>    include/rdma/ib_umem.h                     | 11 +++++++++++
> >>>>    6 files changed, 31 insertions(+), 29 deletions(-)
> >>> <...>
> >>>
> >>>> @@ -1321,8 +1322,8 @@ struct ib_mr *siw_reg_user_mr(struct ib_pd *pd, u64 start, u64 len,
> >>>>    	struct siw_umem *umem = NULL;
> >>>>    	struct siw_ureq_reg_mr ureq;
> >>>>    	struct siw_device *sdev = to_siw_dev(pd->device);
> >>>> -
> >>>> -	unsigned long mem_limit = rlimit(RLIMIT_MEMLOCK);
> >>>> +	unsigned long num_pages =
> >>>> +		(PAGE_ALIGN(len + (start & ~PAGE_MASK))) >> PAGE_SHIFT;
> >>>>    	int rv;
> >>>>    	siw_dbg_pd(pd, "start: 0x%pK, va: 0x%pK, len: %llu\n",
> >>>> @@ -1338,19 +1339,15 @@ struct ib_mr *siw_reg_user_mr(struct ib_pd *pd, u64 start, u64 len,
> >>>>    		rv = -EINVAL;
> >>>>    		goto err_out;
> >>>>    	}
> >>>> -	if (mem_limit != RLIM_INFINITY) {
> >>>> -		unsigned long num_pages =
> >>>> -			(PAGE_ALIGN(len + (start & ~PAGE_MASK))) >> PAGE_SHIFT;
> >>>> -		mem_limit >>= PAGE_SHIFT;
> >>>> -		if (num_pages > mem_limit - current->mm->locked_vm) {
> >>>> -			siw_dbg_pd(pd, "pages req %lu, max %lu, lock %lu\n",
> >>>> -				   num_pages, mem_limit,
> >>>> -				   current->mm->locked_vm);
> >>>> -			rv = -ENOMEM;
> >>>> -			goto err_out;
> >>>> -		}
> >>>> +	if (!ib_umem_check_rlimit_memlock(num_pages + current->mm->locked_vm)) {
> >>>> +		siw_dbg_pd(pd, "pages req %lu, max %lu, lock %lu\n",
> >>>> +				num_pages, rlimit(RLIMIT_MEMLOCK),
> >>>> +				current->mm->locked_vm);
> >>>> +		rv = -ENOMEM;
> >>>> +		goto err_out;
> >>>>    	}
> >>> Sorry for late response, but why does this hunk exist in first place?
> >>>
> 
> Trailing newline, will definitely drop it.
> 
> >>>> +
> >>>>    	umem = siw_umem_get(start, len, ib_access_writable(rights));
> >>> This should be ib_umem_get().
> >>
> >> IMO, it deserves a separate patch, and replace siw_umem_get with ib_umem_get
> >> is not straightforward given siw_mem has two types of memory (pbl and umem).
> > 
> > The thing is that once you convince yourself that SIW should use ib_umem_get(),
> > the same question will arise for other parts of this patch where
> > ib_umem_check_rlimit_memlock() is used.
> > 
> > And if we eliminate them all, there won't be a need for this new API call at all.
> > 
> > Thanks
> >
> 
> Hi!
> 
> So, as for 31.10.2023 I still see siw_umem_get() call used in
> linux-rdma repo in "for-next" branch.

I hoped to hear some feedback from Bernard and Dennis.

> 
> AFAIU this helper call is used only in a single place and could
> potentially be replaced with ib_umem_get() as Leon suggests.
> 
> But should we perform it right inside this memlock helper patch?
> 
> I can submit later another patch with siw_umem_get() replaced
> if necessary.
> 
> 
> >>
> >> Thanks,
> >> Guoqing
>