netdev - Re: [PATCH 1/1] net/rds: suppress page allocation failure error in recv buffer refill

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Date:   Wed, 16 Sep 2020 14:15:08 -0700
From:   Manjunath Patil <manjunath.b.patil@...cle.com>
To:     santosh.shilimkar@...cle.com
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        aruna.ramakrishna@...cle.com, rama.nichanamatlu@...cle.com
Subject: Re: [PATCH 1/1] net/rds: suppress page allocation failure error in
 recv buffer refill

Hi Santosh,

inline.
On 9/16/2020 12:27 PM, santosh.shilimkar@...cle.com wrote:
> On 9/16/20 12:08 PM, Manjunath Patil wrote:
>> RDS/IB tries to refill the recv buffer in softirq context using
>> GFP_NOWAIT flag. However alloc failure is handled by queueing a work to
>> refill the recv buffer with GFP_KERNEL flag. This means failure to
>> allocate with GFP_NOWAIT isn't fatal. Do not print the PAF warnings if
>> softirq context fails to refill the recv buffer, instead print a one
>> line warning once a day.
>>
>> Signed-off-by: Manjunath Patil <manjunath.b.patil@...cle.com>
>> Reviewed-by: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
>> ---
>>   net/rds/ib_recv.c | 16 +++++++++++++---
>>   1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c
>> index 694d411dc72f..38d2894f6bb2 100644
>> --- a/net/rds/ib_recv.c
>> +++ b/net/rds/ib_recv.c
>> @@ -310,8 +310,8 @@ static int rds_ib_recv_refill_one(struct 
>> rds_connection *conn,
>>       struct rds_ib_connection *ic = conn->c_transport_data;
>>       struct ib_sge *sge;
>>       int ret = -ENOMEM;
>> -    gfp_t slab_mask = GFP_NOWAIT;
>> -    gfp_t page_mask = GFP_NOWAIT;
>> +    gfp_t slab_mask = gfp;
>> +    gfp_t page_mask = gfp;
>>         if (gfp & __GFP_DIRECT_RECLAIM) {
>>           slab_mask = GFP_KERNEL;
>> @@ -406,6 +406,16 @@ void rds_ib_recv_refill(struct rds_connection 
>> *conn, int prefill, gfp_t gfp)
>>           recv = &ic->i_recvs[pos];
>>           ret = rds_ib_recv_refill_one(conn, recv, gfp);
>>           if (ret) {
>> +            static unsigned long warn_time;
> Comment should start on next line.
I will add new line. checkpatch.pl didn't find it though.
>> +            /* warn max once per day. This should be enough to
>> +             * warn users about low mem situation.
>> +             */
>> +            if (printk_timed_ratelimit(&warn_time,
>> +                           24 * 60 * 60 * 1000))
>> +                pr_warn("RDS/IB: failed to refill recv buffer for 
>> <%pI6c,%pI6c,%d>, waking worker\n",
>> +                    &conn->c_laddr, &conn->c_faddr,
>> +                    conn->c_tos);
> Didn't notice this before.
> Why not just use "pr_warn_ratelimited()" ?
I think you meant, get rid of if clause and use "pr_warn_ratelimited()" 
instead.
That can still produce more than needed logs during low memory situation.

-Thanks,
Manjunath
>> +
>>               must_wake = true;
>>               break;
>>           }
>> @@ -1020,7 +1030,7 @@ void rds_ib_recv_cqe_handler(struct 
>> rds_ib_connection *ic,
>>           rds_ib_stats_inc(s_ib_rx_ring_empty);
>>         if (rds_ib_ring_low(&ic->i_recv_ring)) {
>> -        rds_ib_recv_refill(conn, 0, GFP_NOWAIT);
>> +        rds_ib_recv_refill(conn, 0, GFP_NOWAIT | __GFP_NOWARN);
>>           rds_ib_stats_inc(s_ib_rx_refill_from_cq);
>>       }
>>   }
>>