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Mon, 27 Apr 2026 14:10:56 +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 Lg9sCHBu72mEBAAAD6G6ig (envelope-from ); Mon, 27 Apr 2026 14:10:56 +0000 Date: Mon, 27 Apr 2026 16:10:54 +0200 From: David Sterba To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH RFC 0/5] btrfs: support huge data folios for 4K page size Message-ID: <20260427141054.GN12792@twin.jikos.cz> Reply-To: dsterba@suse.cz References: Precedence: bulk X-Mailing-List: linux-btrfs@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: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spamd-Result: default: False [-4.00 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; HAS_REPLYTO(0.30)[dsterba@suse.cz]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[twin.jikos.cz:mid,imap1.dmz-prg2.suse.org:helo,suse.cz:replyto]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; REPLYTO_ADDR_EQ_FROM(0.00)[]; REPLYTO_DOM_NEQ_TO_DOM(0.00)[] X-Spam-Flag: NO X-Spam-Score: -4.00 X-Spam-Level: On Fri, Apr 24, 2026 at 06:21:29PM +0930, Qu Wenruo wrote: > [REASON FOR RFC] > > - Unstable baseline for-next branch > The current for-next branch has a known regression where > btrfs_async_reclaim_metadata_space() kworker can fall into a dead loop > and fail several ENOSPC test cases. > Although the regression is pinned down, I'm still waiting for a good > baseline to rebase the series. This has been resolved, patch removed from for-next. > > - Extra on-stack memory usage > Currently we have two bitmaps that are using extra on-stack memory. > Each of them uses 64 bytes on-stack memory, so in total we can have > 128 bytes just for the bitmaps. > > Not sure if it's a concern. This will probably end up in the io path so it can be noticeable but as we've been saving the stack bytes for some time I hope we can afford to use as much as 128 bytes. Allocation on IO path is worse problem in case we have to write data to free more memory. > - Uncertainty related to v7.2 large folio support > I'm planning to move large data folio support out of experimental. > So when that support is no longer experimental, this huge folio support > would need to start as experimental I'd rather enable them separately. The large folios will affect everything so we should minimize potential problems with another feature. > Depends on which patch(set) is merged first, there needs to be some > modification to ensure end users won't suddenly get not only large but > also huge folios. As rc1 is out we can start enabling fetures for 7.2, so please add the large folios by default and the THP support as experimental.