On Tue, May 09, 2023 at 02:12:41PM -0700, Lorenzo Stoakes wrote: > On Tue, May 09, 2023 at 01:46:09PM -0700, Christoph Hellwig wrote: > > On Tue, May 09, 2023 at 12:56:32PM -0400, Kent Overstreet wrote: > > > From: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > > > > > This is needed for bcachefs, which dynamically generates per-btree node > > > unpack functions. > > > > No, we will never add back a way for random code allocating executable > > memory in kernel space. > > Yeah I think I glossed over this aspect a bit as it looks ostensibly like simply > reinstating a helper function because the code is now used in more than one > place (at lsf/mm so a little distracted :) > > But it being exported is a problem. Perhaps there's another way of acheving the > same aim without having to do so? None that I see. The background is that bcachefs generates a per btree node unpack function, based on the packed format for that btree node, for unpacking keys within that node. The unpack function is only ~50 bytes, and for locality we want it to be located with the btree node's other in-memory lookup tables so they can be prefetched all at once. Here's the codegen: https://evilpiepirate.org/git/bcachefs.git/tree/fs/bcachefs/bkey.c#n727
