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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Queue-Id: 6FA36C0007 X-Stat-Signature: 89rdo68yekusjz5ncyh8i8ixbm4yjrck X-Rspamd-Server: rspam06 X-HE-Tag: 1779306329-873332 X-HE-Meta: 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 s2Oe09q8 beogLKSmlWst5PLBFlfKV++j4/7dkUKfEebUGPlMhoQpAWLa6gsjrURDAXKLF9N8Lt12fpC7UUYMbau932ugLvChWNqdcguxkF5wN25HSPPimgP+pcryA98Z94ejEE2ion3Mz9XK60zWfHXruZrJtWt5yyf+cZrYtTC/YJq61HdvsTP+NfsOpnVl9Flv3+i3GWpAr90rQHuc4tSt4ayUeustf9e7Ole1uyTjlxann9qecuRA69Z0zKD1DbFQBLOTE5leVR+umisQOWB9gnbUZjeNcrFBvBFuO+DH454suW1WnMohFhhBAzWHMVJaxO2UofLwL Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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