linux-kernel - Re: [PATCH 00/11] scsi: libsas: Remove in

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Date:   Mon, 11 Jan 2021 13:59:25 +0000
From:   John Garry <john.garry@...wei.com>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Jason Yan <yanaijie@...wei.com>
CC:     Hannes Reinecke <hare@...e.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Daniel Wagner <dwagner@...e.de>,
        Artur Paszkiewicz <artur.paszkiewicz@...el.com>,
        Jack Wang <jinpu.wang@...ud.ionos.com>,
        <linux-scsi@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>
Subject: Re: [PATCH 00/11] scsi: libsas: Remove in_interrupt() check

On 11/01/2021 13:43, Ahmed S. Darwish wrote:
> Hi John, Jason,
> 
> On Tue, Dec 22, 2020 at 12:54:58PM +0000, John Garry wrote:
>> On 22/12/2020 12:30, Jason Yan wrote:
>>>>       return event;
>>>>
>>>>
>>>> So default for phy->ha->event_thres is 32, and I can't imagine that
>>> The default value is 1024.
>> Ah, 32 is the minimum allowed set via sysfs.
>>
>>>> anyone has ever reconfigured this via sysfs or even required a value
>>>> that large. Maybe Jason (cc'ed) knows better. It's an arbitrary
>>>> value to say that the PHY is malfunctioning. I do note that there is
>>>> the circular path sas_alloc_event() -> sas_notify_phy_event() ->
>>>> sas_alloc_event() there also.
>>>>
>>>> Anyway, if the 32x event memories were per-allocated, maybe there is
>>>> a clean method to manage this memory, which even works in atomic
>>>> context, so we could avoid this rework (ignoring the context bugs
>>>> you reported for a moment). I do also note that the sas_event_cache
>>>> size is not huge.
>>>>
>>> Pre-allocated memory is an option.(Which we have tried at the very
>>> beginnig by Wang Yijing.)
>> Right, I remember this, but I think the concern was having a proper method
>> to manage this pre-allocated memory then. And same problem now.
>>
>>> Or directly use GFP_ATOMIC is maybe better than passing flags from lldds.
>>>
>> I think that if we don't really need this, then should not use it.
>>
> Kind reminder. Do we have any consensus here?
> 

Hi Ahmed,

To me, what you're doing seems fine.

I was looking for some API to manage small memory pools and which is 
atomic safe to avoid passing the context flag, but I didn't find such a 
thing.

Just one other thing to mention:
I have a patch to remove the indirection in libsas notifiers:
https://github.com/hisilicon/kernel-dev/commit/87fcd7e113dc05b7933260e7fa4588dc3730cc2a

I was going to send it today. Hopefully, if community has no problem 
with it, you can make your changes with that in mind.

Thanks,
John