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a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1750337216; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5+fM4MttKE3A03nChZO9COV7itbt2Km8YxBW6g7esUo=; b=Z3lXv73KiWY95pdfmh0Pfoybb2uI7JQ/GOM/KUE+4HCpm8wNwpLgJVMr1jyxA1mQ0kYTdq qo5CPob2oAwOuLqoPwuED71JRJlAKPh3UsqRt2Z2LXvQsvTlhOw5o4axHBOq6Iet9J7Zqz llCXE56uDd/TA5E44rbeitRFwFNHgKg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1750337216; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5+fM4MttKE3A03nChZO9COV7itbt2Km8YxBW6g7esUo=; b=5FlSBCrgaDGDUb9oa6w9IwyKfAfRQrd/oRtVGPljTKwpZAGsn5pONnUfbtqkNDE6Q1xbJR wBFaHrGrQ5zF6cBQ== Date: Thu, 19 Jun 2025 14:46:56 +0200 From: Jiri Bohac To: Andrew Morton Cc: David Hildenbrand , Baoquan He , Vivek Goyal , Dave Young , kexec@lists.infradead.org, Philipp Rudo , Donald Dutile , Pingfan Liu , Tao Liu , linux-kernel@vger.kernel.org, David Hildenbrand , Michal Hocko Subject: Re: [PATCH v5 4/5] kdump: wait for DMA to finish when using CMA Message-ID: References: <20250612164735.76a1ea9a156cd254331ffdc4@linux-foundation.org> <925cdfc4-7878-4572-9a4d-9b99d149a652@redhat.com> 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: <925cdfc4-7878-4572-9a4d-9b99d149a652@redhat.com> X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[13]; ARC_NA(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; MID_RHS_MATCH_FROMTLD(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[localhost:helo] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -4.30 On Fri, Jun 13, 2025 at 11:19:11AM +0200, David Hildenbrand wrote: > > It's sad to add a 10s delay for something which some systems will never > > do. I wonder if there's some simple hack we can add. Like having a > > global flag which gets set the first time someone pins a CMA page > > We would likely have to do that for any GUP on such a page (FOLL_GET | > FOLL_PIN), both from gup-fast and gup-slow. > > Should work, but IMHO can be optimized later, on top of this series. The 10 s was David's suggestion during the discussion of v2 of this patchset. We already had a discussion about both the length of the delay and whether to make it configurable [1] We agreed it was best to start with a longer fixed delay to be on the safe side. If the CMA reservation becomes popular and anybody complains about the delay, then we can trivially make this configurable or think of other improvements. [1] https://lore.kernel.org/lkml/a1a5af90-bc8a-448a-81fa-485624d592f3@redhat.com/ -- Jiri Bohac SUSE Labs, Prague, Czechia