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From: Kent Overstreet To: Eric Biggers Cc: Lorenzo Stoakes , 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: <20230510064849.GC1851@quark.localdomain> <20230513015752.GC3033@quark.localdomain> <20230514184325.GB9528@sol.localdomain> <20230515061346.GB15871@sol.localdomain> <20230515071343.GD15871@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230515071343.GD15871@sol.localdomain> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: oits3zedndp4u7rd34r89n3sy3c3ypgy X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 57C8514000D X-HE-Tag: 1684135610-428014 X-HE-Meta: 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 EUj/4ubV 88cP0yb5lxqylECkoWjRvP/XUqByNqQDmWeAxCtVZvFiw9mt40Qu5wWGmmPA8mVVoeCHfJU10vboCTzt3OAj7S6J1dzsnZJB5MaZ8+x7XPzeFx9DxTbI5A+zcMVAC4xZL2Y0q/igvdY6yjVhscxBtl0Y4s6AFRTskykFM 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 Mon, May 15, 2023 at 12:13:43AM -0700, Eric Biggers wrote: > Sure, given that this is an optimization problem with a very small scope > (decoding 6 fields from a bitstream), I was hoping for something easier and > faster to iterate on than setting up a full kernel + bcachefs test environment > and reverse engineering 500 lines of shell script. But sure, I can look into > that when I have a chance. If you were actually wanting to help, that repository is the tool I use for kernel development and testing - it's got documentation. It builds a kernel, boots a VM and runs a test in about 15 seconds, no need for lifting that code out to userspace. > > Your approach wasn't any faster than the existing C version. > > Well, it's your implementation of what you thought was "my approach". It > doesn't quite match what I had suggested. As I mentioned in my last email, it's > also unclear that your new code is ever actually executed, since you made it > conditional on all fields being byte-aligned... Eric, I'm not an idiot, that was one of the first things I checked. No unaligned bkey formats were generated in my tests. The latest iteration of your approach that I looked at compiled to ~250 bytes of code, vs. ~50 bytes for the dynamically generated unpack functions. I'm sure it's possible to shave a bit off with some more work, but looking at the generated code it's clear it's not going to be competitive.