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

[Leon Romanovsky <leon@kernel.org>]

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?
> > 
> > > +
> > >   	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

> 
> Thanks,
> Guoqing