linux-kernel - [PATCH net] RDMA/umem: add a schedule point in ib_umem

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Date:   Wed, 29 Jul 2020 18:57:55 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        linux-rdma@...r.kernel.org
Subject: [PATCH net] RDMA/umem: add a schedule point in ib_umem_get()

Mapping as little as 64GB can take more than 10 seconds,
triggering issues on kernels with CONFIG_PREEMPT_NONE=y.

ib_umem_get() already splits the work in 2MB units on x86_64,
adding a cond_resched() in the long-lasting loop is enough
to solve the issue.

Note that sg_alloc_table() can still use more than 100 ms,
which is also problematic. This might be addressed later
in ib_umem_add_sg_table(), adding new blocks in sgl
on demand.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Doug Ledford <dledford@...hat.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-rdma@...r.kernel.org
---
 drivers/infiniband/core/umem.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 82455a1392f1d19c96ae956f0bd4e93e3a52d29c..831bff8d52e547834e9e04064127fbb280595126 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -261,6 +261,7 @@ struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 	sg = umem->sg_head.sgl;
 
 	while (npages) {
+		cond_resched();
 		ret = pin_user_pages_fast(cur_base,
 					  min_t(unsigned long, npages,
 						PAGE_SIZE /
-- 
2.28.0.rc0.142.g3c755180ce-goog