linux-ext4 - Re: [PATCH v6 05/13] drm/amdkfd: generic type as sys mem on migration to ram

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Date:   Mon, 16 Aug 2021 14:53:18 -0500
From:   "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     akpm@...ux-foundation.org, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        jgg@...dia.com, jglisse@...hat.com
Subject: Re: [PATCH v6 05/13] drm/amdkfd: generic type as sys mem on migration
 to ram


On 8/15/2021 10:38 AM, Christoph Hellwig wrote:
> On Fri, Aug 13, 2021 at 01:31:42AM -0500, Alex Sierra wrote:
>>   	migrate.vma = vma;
>>   	migrate.start = start;
>>   	migrate.end = end;
>> -	migrate.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;
>>   	migrate.pgmap_owner = SVM_ADEV_PGMAP_OWNER(adev);
>>   
>> +	if (adev->gmc.xgmi.connected_to_cpu)
>> +		migrate.flags = MIGRATE_VMA_SELECT_SYSTEM;
>> +	else
>> +		migrate.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;
> It's been a while since I touched this migrate code, but doesn't this
> mean that if the range already contains system memory the migration
> now won't do anything? for the connected_to_cpu case?

For above’s condition equal to connected_to_cpu , we’re explicitly 
migrating from
device memory to system memory with device generic type. In this type, 
device PTEs are
present in CPU page table.

During migrate_vma_collect_pmd walk op at migrate_vma_setup call, 
there’s a condition
for present pte that require migrate->flags be set for 
MIGRATE_VMA_SELECT_SYSTEM.
Otherwise, the migration for this entry will be ignored.

Regards,
Alex S.