linux-kernel - RE: [PATCH net-next] net: mana: Improve mana_set

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Message-ID:
 <PH7PR21MB32606D2D49A7F0837A29835DCA962@PH7PR21MB3260.namprd21.prod.outlook.com>
Date: Thu, 29 Aug 2024 21:00:05 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Gerhard Engleder <gerhard@...leder-embedded.com>, Shradha Gupta
	<shradhagupta@...ux.microsoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-rdma@...r.kernel.org"
	<linux-rdma@...r.kernel.org>
CC: KY Srinivasan <kys@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, Dexuan
 Cui <decui@...rosoft.com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Long Li <longli@...rosoft.com>, Simon Horman
	<horms@...nel.org>, Konstantin Taranov <kotaranov@...rosoft.com>, Souradeep
 Chakrabarti <schakrabarti@...ux.microsoft.com>, Erick Archer
	<erick.archer@...look.com>, Pavan Chebbi <pavan.chebbi@...adcom.com>, Ahmed
 Zaki <ahmed.zaki@...el.com>, Colin Ian King <colin.i.king@...il.com>, Shradha
 Gupta <shradhagupta@...rosoft.com>
Subject: RE: [PATCH net-next] net: mana: Improve mana_set_channels() for low
 mem conditions



> -----Original Message-----
> From: Gerhard Engleder <gerhard@...leder-embedded.com>
> Sent: Thursday, August 29, 2024 3:54 PM
> To: Shradha Gupta <shradhagupta@...ux.microsoft.com>; linux-
> hyperv@...r.kernel.org; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; linux-rdma@...r.kernel.org
> Cc: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; Wei Liu <wei.liu@...nel.org>; Dexuan Cui
> <decui@...rosoft.com>; David S. Miller <davem@...emloft.net>; Eric
> Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo
> Abeni <pabeni@...hat.com>; Long Li <longli@...rosoft.com>; Simon Horman
> <horms@...nel.org>; Konstantin Taranov <kotaranov@...rosoft.com>;
> Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>; Erick Archer
> <erick.archer@...look.com>; Pavan Chebbi <pavan.chebbi@...adcom.com>;
> Ahmed Zaki <ahmed.zaki@...el.com>; Colin Ian King
> <colin.i.king@...il.com>; Shradha Gupta <shradhagupta@...rosoft.com>
> Subject: Re: [PATCH net-next] net: mana: Improve mana_set_channels() for
> low mem conditions
> 
> [Some people who received this message don't often get email from
> gerhard@...leder-embedded.com. Learn why this is important at
> https://aka.ms/LearnAboutSenderIdentification ]
> 
> On 29.08.24 16:16, Shradha Gupta wrote:
> > The mana_set_channels() function requires detaching the mana
> > driver and reattaching it with changed channel values.
> > During this operation if the system is low on memory, the reattach
> > might fail, causing the network device being down.
> > To avoid this we pre-allocate buffers at the beginning of set
> operation,
> > to prevent complete network loss
> >
> > Signed-off-by: Shradha Gupta <shradhagupta@...ux.microsoft.com>
> > ---
> >   .../ethernet/microsoft/mana/mana_ethtool.c    | 28 +++++++++++-------
> -
> >   1 file changed, 16 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
> b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
> > index d6a35fbda447..5077493fdfde 100644
> > --- a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
> > +++ b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
> > @@ -345,27 +345,31 @@ static int mana_set_channels(struct net_device
> *ndev,
> >       struct mana_port_context *apc = netdev_priv(ndev);
> >       unsigned int new_count = channels->combined_count;
> >       unsigned int old_count = apc->num_queues;
> > -     int err, err2;
> > +     int err;
> > +
> > +     apc->num_queues = new_count;
> > +     err = mana_pre_alloc_rxbufs(apc, ndev->mtu);
> > +     apc->num_queues = old_count;
> 
> Are you sure that temporary changing num_queues has no side effects on
> other num_queues users like mana_chn_setxdp()?
> 

mana_chn_setxdp() is protected by rtnl_lock, which is OK. But I'm not sure
if all other users are protected. mana_get_stats64() seems not.

@Shradha Gupta You can add num_queues as an argument of mana_pre_alloc_rxbufs()
to avoid changing apc->num_queues.

Thanks,
- Haiyang