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

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Message-ID: <2672812e-91bd-4c60-696d-4000b1914ac6@huawei.com>
Date:   Tue, 22 Dec 2020 12:54:58 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jason Yan <yanaijie@...wei.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "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>
CC:     <linux-scsi@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH 00/11] scsi: libsas: Remove in_interrupt() check

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.

Thanks,
John