linux-kernel - Re: [PATCH v36 2/5] virtio_balloon: replace oom notifier with shrinker

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Date:   Tue, 24 Jul 2018 09:49:20 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...nel.org, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, pbonzini@...hat.com,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu0@...il.com, nilal@...hat.com, riel@...hat.com,
        peterx@...hat.com
Subject: Re: [PATCH v36 2/5] virtio_balloon: replace oom notifier with shrinker

On 07/23/2018 10:13 PM, Michael S. Tsirkin wrote:
>>>    	vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
>>>    #endif
>>> +	err = virtio_balloon_register_shrinker(vb);
>>> +	if (err)
>>> +		goto out_del_vqs;
>>> So we can get scans before device is ready. Leak will fail
>>> then. Why not register later after device is ready?
>> Probably no.
>>
>> - it would be better not to set device ready when register_shrinker failed.
> That's very rare so I won't be too worried.

Just a little confused with the point here. "very rare" means it still 
could happen (even it's a corner case), and if that happens, we got 
something wrong functionally. So it will be a bug if we change like 
that, right?

Still couldn't understand the reason of changing shrinker_register after 
device_ready (the original oom notifier was registered before setting 
device ready too)?
(I think the driver won't get shrinker_scan called if device isn't ready 
because of the reasons below)

>> - When the device isn't ready, ballooning won't happen, that is,
>> vb->num_pages will be 0, which results in shrinker_count=0 and shrinker_scan
>> won't be called.

Best,
Wei