On Wed, Sep 30, 2020 at 01:27:45PM +0300, Mike Rapoport wrote: > On Tue, Sep 29, 2020 at 05:15:52PM +0200, Peter Zijlstra wrote: > > On Tue, Sep 29, 2020 at 05:58:13PM +0300, Mike Rapoport wrote: > > > On Tue, Sep 29, 2020 at 04:12:16PM +0200, Peter Zijlstra wrote: > > > > > > It will drop them down to 4k pages. Given enough inodes, and allocating > > > > only a single sekrit page per pmd, we'll shatter the directmap into 4k. > > > > > > Why? Secretmem allocates PMD-size page per inode and uses it as a pool > > > of 4K pages for that inode. This way it ensures that > > > __kernel_map_pages() is always called on PMD boundaries. > > > > Oh, you unmap the 2m page upfront? I read it like you did the unmap at > > the sekrit page alloc, not the pool alloc side of things. > > > > Then yes, but then you're wasting gobs of memory. Basically you can pin > > 2M per inode while only accounting a single page. > > Right, quite like THP :) Huh? THP accounts every page it allocates. If you allocate 2MB, it accounts 512 pages. And THP are reclaimable by vmscan, this is obviously not.
