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From: Kent Overstreet To: Lorenzo Stoakes Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-bcachefs@vger.kernel.org, Kent Overstreet , Andrew Morton , Uladzislau Rezki , linux-mm@kvack.org Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec Message-ID: References: <20230509165657.1735798-1-kent.overstreet@linux.dev> <20230509165657.1735798-8-kent.overstreet@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: wxy49c314jbnyoy6c8qy5xa9xpb8ys79 X-Rspam-User: X-Rspamd-Queue-Id: 9891410000F X-Rspamd-Server: rspam07 X-HE-Tag: 1683667756-416204 X-HE-Meta: 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 idnmvdly 2Q+zwiCaZ+h2sskzWATi/o/lPgUfrEx89+dAIWBpRU9yW4OXdke9MOIL0+95Hqwsnb0vseL/14s4rqHsMifL3vod23Fp7ErIyBHW9WyKg06W0pICVzZeYIw9qoRAYur5Wkd9I/QVDmvA5DGReutXE246EfwZRfgBAJ27mzD3AvBTunPlwM0A/hOFUu9BAGl42udnvxEBd0kvbFTZHvoRBAWHn3HRq8VNl2ihwQ2Um23/D/QEcU9HExgfgEw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > > > > > > 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