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Wed, 20 May 2026 19:45:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id dZjnIlcPDmodJwAAD6G6ig (envelope-from ); Wed, 20 May 2026 19:45:27 +0000 Date: Wed, 20 May 2026 21:45:22 +0200 From: Pedro Falcato To: Daniel Palmer Cc: Lorenzo Stoakes , akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mm/nommu: Implement just enough vmap that compressed erofs can be mounted Message-ID: References: <20260520163442.1099667-1-daniel@thingy.jp> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Flag: NO X-Spam-Score: -4.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DWL_DNSWL_BLOCKED(0.00)[suse.de:dkim]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: A9D9866D8A X-Spam-Level: On Thu, May 21, 2026 at 02:22:25AM +0900, Daniel Palmer wrote: > Hi Lorenzo, (and Pedro), > > On Thu, 21 May 2026 at 02:05, Lorenzo Stoakes wrote: > > > > For some reason this iddn't arrive in my inbox properly... strange? Maybe > > missing To:? > > Sorry, I CC'd everyone hoping I wouldn't get grilled for the silly patch. > > > > Did I miss anything massive that is going to come back and bite me? > > > Maybe it would have made more sense just to change the erofs > > > code so on !CONFIG_MMU it doesn't use vmap? > > > > I think that'd probably be better honestly. I think faking out vmalloc is more > > trouble than it's worth, and it'd probably have to be everything-or-nothing. > > That makes sense. > Do you think it'd be acceptable to maybe return NULL from these > functions instead of crashing the kernel? I suspect the reason for this is simple: calling these functions in !mmu configs is a programming mistake, and we want it to blow up loudly instead of having slightly/very broken behavior. Maybe in 2026 we'd have picked WARN_ON() + return NULL. But I don't think it makes too much sense here, honestly. > > > But yeah would gently point you towards doing something on the fs end I think > > here :) > > Noted. I think I'll at least send them a patch to make compression > support depend on CONFIG_MMU. Awesome! (note: since you're space restricted you may actually want that compression :p) -- Pedro