Messages in this thread | | | Subject | Re: [PATCH v3 1/3] mm: document zone device struct page field usage | From | Ralph Campbell <> | Date | Thu, 25 Jul 2019 11:19:07 -0700 |
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On 7/24/19 10:38 PM, Christoph Hellwig wrote: > On Wed, Jul 24, 2019 at 04:26:58PM -0700, Ralph Campbell wrote: >> Struct page for ZONE_DEVICE private pages uses the page->mapping and >> and page->index fields while the source anonymous pages are migrated to >> device private memory. This is so rmap_walk() can find the page when >> migrating the ZONE_DEVICE private page back to system memory. >> ZONE_DEVICE pmem backed fsdax pages also use the page->mapping and >> page->index fields when files are mapped into a process address space. >> >> Add comments to struct page and remove the unused "_zd_pad_1" field >> to make this more clear. > > I still think we should also fix up the layout, and I haven't seen > a reply from Matthew justifying his curses for your patch that makes > the struct page layout actually match how it is used. >
Well, I can kind of see this both ways since ZONE_DEVICE MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA don't seem to use the 3 words like MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_FS_DAX.
I like v3 because not all of the ZONE_DEVICE types are handled the same in regards to using the 3 words and there may be future ZONE_DEVICE types that use the 3 words differently which might require a union.
I agree, I would like to hear from Matthew on his thoughts.
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