On Mon, Jan 17, 2022 at 04:10:46PM +0000, Matthew Wilcox wrote: > On Mon, Jan 17, 2022 at 07:06:25PM +0300, Kirill A. Shutemov wrote: > > On Sun, Jan 16, 2022 at 12:18:14PM +0000, Matthew Wilcox (Oracle) wrote: > > > We have to allocate memory in order to split a file-backed folio, so > > > it's not a good idea to split them in the memory freeing path. > > > > Could elaborate on why split a file-backed folio requires memory > > allocation? > > In the commit message or explain it to you now? > > We need to allocate xarray nodes to store all the newly-independent > pages. With a folio that's more than 64 entries in size (current > implementation), we elide the lowest layer of the radix tree. But > with any data structure that tracks folios, we'll need to create > space in it to track N folios instead of 1. Looks good. > > > It also > > > doesn't work for XFS because pages have an extra reference count from > > > page_has_private() and split_huge_page() expects that reference to have > > > already been removed. > > > > Need to adjust can_split_huge_page()? > > no? I meant we can make can_split_huge_page() expect extra pin if page_has_private() is true. If it is the only thing that stops split_huge_page() from handling XFS pages. -- Kirill A. Shutemov
