On Wed, 2020-09-30 at 13:27 +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 :) > > I considered using a global pool of 2M pages for secretmem and > handing 4K pages to each inode from that global pool. But I've > decided to waste memory in favor of simplicity. I can also add that the user space consumer of this we wrote does its user pool allocation at a 2M granularity, so nothing is actually wasted. https://git.kernel.org/pub/scm/linux/kernel/git/jejb/secret-memory-preloader.git/ James
