Re: [PATCH 14/15] dax: associate mappings with inodes, and warn if dma collides with truncate

On Fri, Nov 10, 2017 at 1:08 AM, Christoph Hellwig <hch(a)lst.de&gt; wrote: >> + struct { >> + /* >> + * ZONE_DEVICE pages are never on an lru or handled by >> + * a slab allocator, this points to the hosting device >> + * page map. >> + */ >> + struct dev_pagemap *pgmap; >> + /* >> + * inode association for MEMORY_DEVICE_FS_DAX page-idle >> + * callbacks. Note that we don't use ->mapping since >> + * that has hard coded page-cache assumptions in >> + * several paths. >> + */ > > What assumptions? I'd much rather fix those up than having two fields > that have the same functionality. [ Reviving this old thread where you asked why I introduce page->inode instead of reusing page->mapping ] For example, xfs_vm_set_page_dirty() assumes that page->mapping being non-NULL indicates a typical page cache page, this is a false assumption for DAX.

My guess at a fix for this is to add pagecache_page() checks to locations like this, but I worry about how to find them all. Where pagecache_page() is: bool pagecache_page(struct page *page) { if (!page->mapping) return false; if (!IS_DAX(page->mapping->host)) return false; return true; }