From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 08F0920FA98 for ; Wed, 19 Mar 2025 21:18:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742419138; cv=none; b=mUulNylW9jnSWCCwcrWCfmf947gR6qQYgosmg7ijK8FcesxcGRRH4oVsfP6fsdNGdrJogDlt3pY9EFLtGMlJxIH0Ng/D90YNTi8voceIwcc0Y3a46mOf6qz+3wzl1MwQxMjyDsl+stYUzhnnCpVEtmQTddbkQVvhKOV4Oprod7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742419138; c=relaxed/simple; bh=8Qk21XtAtuMr8WU/6FPqNPIz8trBEboe6geXCafiXGo=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=g2JXvDuwdfVKg42RQ/AD9ynAsrCsogokPBk0Fkxcg7OZjIv25Y5+BweYNWyTDREW2DOIVTLhloivmeAC1GTfNNxRquL3Kym6iLA65uTXKr2LNLq66vzcpoYF7QwUVP3g7R4QFKh5//0zRw9nI6xgMn7qkQG5pFtC1H88bvEhvbw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=FTEV93bX; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FTEV93bX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742419134; h=from:from:reply-to:subject:subject: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=yANbqU707rXdx8XQYm6bZXg9kJ9aFMXd583FayRRhY0=; b=FTEV93bXDYwPNVnDsF40jr7aqRbTtF8BlSxnrtI64s5L0KRpkY+UvUQisch/Bd3e0Ajhfo Q3m4xpEnndKHIjEPEaaYtOaH7wlqYU4kU/u7saJoJSOnYvXUq6TWiDLdOrMlXWYO1XxxUM pH95rex9t25LeihbOfAhGdqrDjc+r3I= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-29-C9pNz4odPf6XF8mc9B_G6Q-1; Wed, 19 Mar 2025 17:18:49 -0400 X-MC-Unique: C9pNz4odPf6XF8mc9B_G6Q-1 X-Mimecast-MFC-AGG-ID: C9pNz4odPf6XF8mc9B_G6Q_1742419128 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C545F1801A00; Wed, 19 Mar 2025 21:18:47 +0000 (UTC) Received: from [10.22.82.75] (unknown [10.22.82.75]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 750C11800370; Wed, 19 Mar 2025 21:18:44 +0000 (UTC) Date: Wed, 19 Mar 2025 22:18:39 +0100 (CET) From: Mikulas Patocka To: Jens Axboe cc: Ming Lei , Alasdair Kergon , Mike Snitzer , linux-block@vger.kernel.org, dm-devel@lists.linux.dev Subject: Re: [PATC] block: update queue limits atomically In-Reply-To: <6ebdd2ae-8fc2-4072-b131-a7c0da56d3f2@kernel.dk> Message-ID: References: <6ebdd2ae-8fc2-4072-b131-a7c0da56d3f2@kernel.dk> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Tue, 18 Mar 2025, Jens Axboe wrote: > > Yeah, it looks fine, but I feel it is still fragile, and not sure it is one > > accepted solution. > > Agree - it'd be much better to have the bio drivers provide the same > guarantees that we get on the request side, rather than play games with > this and pretend that concurrent update and usage is fine. > > -- > Jens Axboe And what mechanism should they use to read the queue limits? * locking? (would degrade performance) * percpu-rwsem? (no overhead for readers, writers wait for the RCU synchronization) * RCU? * anything else? Mikulas