On Mon, Apr 07, 2025 at 10:11:08PM -0700, Christoph Hellwig wrote: > On Mon, Apr 07, 2025 at 05:30:30PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > Prior to commit e614a00117bc2d, xmbuf_map_backing_mem relied on > > folio_file_page to return the base page for the xmbuf's loff_t in the > > xfile, and set b_addr to the page_address of that base page. > > > > Now that folio_file_page has been removed from xmbuf_map_backing_mem, we > > always set b_addr to the folio_address of the folio. This is correct > > for the situation where the folio size matches the buffer size, but it's > > totally wrong if tmpfs uses large folios. We need to use > > offset_in_folio here. > > > > Found via xfs/801, which demonstrated evidence of corruption of an > > in-memory rmap btree block right after initializing an adjacent block. > > Hmm, I thought we'd never get large folios for our non-standard tmpfs > use. I guess I was wrong on that.. Yeah, you can force THPs for tmpfs. I don't know why you would, the memory usage is gawful on most files that end up in there. > The fix looks good: > > Reviewed-by: Christoph Hellwig <hch@xxxxxx> > > But a little note below: > > > + bp->b_addr = folio_address(folio) + offset_in_folio(folio, pos); > > Given that this is or at least will become a common pattern, do we > want a mm layer helper for it? Yeah, we should; this is the third one in XFS. What to name it, though? void *folio_addr(const struct folio *folio, loff_t pos) ? I'm surprised there wasn't an equivalent for struct page. --D
