From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7922FCFA46B for ; Sun, 23 Nov 2025 20:10:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7F7426B002B; Sun, 23 Nov 2025 15:10:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7809D6B002C; Sun, 23 Nov 2025 15:10:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 66FBE6B002D; Sun, 23 Nov 2025 15:10:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 550A96B002B for ; Sun, 23 Nov 2025 15:10:09 -0500 (EST) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id C9B65140128 for ; Sun, 23 Nov 2025 20:10:08 +0000 (UTC) X-FDA: 84142963296.12.F9FE750 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf25.hostedemail.com (Postfix) with ESMTP id B77D4A0005 for ; Sun, 23 Nov 2025 20:10:06 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AzTXLzjb; spf=pass (imf25.hostedemail.com: domain of oleg@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763928607; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=kCNBLrjOr1foGs26XOE6a2gSNdqIv5bHIjwCsegLTIA=; b=tNC0pQv8SolMR0GakgTlDHQAKplRimIHgmHpIyzQfbZ9OkaMOnCqOmtHk9O7TGvwsxmzYW /m4oDoBBjlbAH577fSAo9RoKnCs734YAxHYpQ+Yrv74gimGuT8PAn0ei0FUdqRBw1hHovc xlii1/ZsdrF1HjnfQ9GwvGDfFkv2MiY= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AzTXLzjb; spf=pass (imf25.hostedemail.com: domain of oleg@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763928607; a=rsa-sha256; cv=none; b=KJBPNmMlglKmy1dJ4S+IRqhkLVbBqtzNIy1gzn10SunkubHeJw8cuwdm6XST+Lp2x/B9+z 4lij24Xwp4FZheYQl7gnC0LX/0tP5XKQKV2rypoulW3cYvK9VJJexXKhdYw8B7l8nTNvt7 7864O5PARS4MdndyjBj4ZoJv09qwbw4= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763928606; 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=kCNBLrjOr1foGs26XOE6a2gSNdqIv5bHIjwCsegLTIA=; b=AzTXLzjbatT3fVpsVkpry2OJRiHaUJFfw0zNd6pedFFx6SgxVghvVnzhTHMhBnH1dGbuW5 c6QDl3RH0hr9ON+im/aB3kQElrTGU3XaPO2hxmpv4V4QOs/yFfLe/Av8YA4zfNJvREmou2 K59GfrBPbfYawPSOBVBMxBCB9QIfQUE= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-88-hZe5QCUTOCOc5Rs5Q6zXug-1; Sun, 23 Nov 2025 15:10:00 -0500 X-MC-Unique: hZe5QCUTOCOc5Rs5Q6zXug-1 X-Mimecast-MFC-AGG-ID: hZe5QCUTOCOc5Rs5Q6zXug_1763928599 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CA10D195608A; Sun, 23 Nov 2025 20:09:58 +0000 (UTC) Received: from fedora (unknown [10.45.224.57]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id B7C091955F1B; Sun, 23 Nov 2025 20:09:56 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 23 Nov 2025 21:09:58 +0100 (CET) Date: Sun, 23 Nov 2025 21:09:55 +0100 From: Oleg Nesterov To: Mateusz Guzik Cc: brauner@kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH 3/3] pid: only take pidmap_lock once on alloc Message-ID: References: <20251123063054.3502938-1-mjguzik@gmail.com> <20251123063054.3502938-4-mjguzik@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251123063054.3502938-4-mjguzik@gmail.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B77D4A0005 X-Stat-Signature: ojqqzbsjff1mtawzz5f5manphiwecfuh X-Rspam-User: X-HE-Tag: 1763928606-417467 X-HE-Meta: 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 cErkepAn juIkvRqzoJWaw7ZyqnF+Vk/B/K/ZPvX9HOdwkDCDQjT4ISBOWxHotvvbpK7v5uwOWGoA7CNsCqlPes6NnCyH01qkNTYDdZRKHAm/5NjxymV5Pxn+8Tra3WFQ3Q88vx7Rc7+rMFcdiy0NYC/137lAs5CgVbRw7bbg5iYvveu9tSSkz4eqM/wNopNHdCS/8F82VSkwGdTgNtOBeh2ib6ABnXY1djfH9GJX2oabMR2ipJW/57m2+aamQJipHb+A6hgzp7eDEMEZgcvmfBV76IB1sOresyjQFnmtxNeRlxepzmjZk0pq7Gzp9Fp76R0vJZfTaBW+OBo24bz0/OUJSVUvC8UcTsPaDSJd8dF7cj4IwLtRuXv7WF1V5M3Wt6xphRjvq62kNfW0oGzopUdY= 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: List-Subscribe: List-Unsubscribe: On 11/23, Mateusz Guzik wrote: > > This reduces contention on the lock during parallel clone/exit. > > It remains the primary bottleneck in such a case. > > While here tidy up the code. Not sure I can review... But FWIW this patch looks good to me after the very quick glance. I'll try to actually read it tomorrow. But please find a couple of minor "can't resist" nits below. > + for (tmp = ns, i = ns->level; i >= 0; i--) { > + int tid = set_tid[ns->level - i]; > > if (tid) { > nr = idr_alloc(&tmp->idr, NULL, tid, > @@ -235,10 +261,8 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, > * a partially initialized PID (see below). > */ > nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min, > - pid_max, GFP_ATOMIC); > + pid_max[ns->level - i], GFP_ATOMIC); > } > - spin_unlock(&pidmap_lock); > - idr_preload_end(); > > if (nr < 0) { > retval = (nr == -ENOSPC) ? -EAGAIN : nr; So. With or without this patch we have if (tid) { nr = idr_alloc(...); if (nr == -ENOSPC) nr = -EEXIST; } else { nr = idr_alloc_cyclic(...); } if (nr < 0) { retval = (nr == -ENOSPC) ? -EAGAIN : nr; goto out_free; } and somehow this looks annoying to me... Perhaps it makes sense to make this code more symmetric (and imo more readable) ? if (tid) { nr = idr_alloc(...); if (nr == -ENOSPC) nr = -EEXIST; } else { nr = idr_alloc_cyclic(...); if (nr == -ENOSPC) nr = -EAGAIN; } if (nr < 0) retval = nr; goto out_free; } > - idr_preload(GFP_KERNEL); > - spin_lock(&pidmap_lock); > - if (!(ns->pid_allocated & PIDNS_ADDING)) > - goto out_unlock; > + if (unlikely(!(ns->pid_allocated & PIDNS_ADDING))) > + goto out_free; > pidfs_add_pid(pid); > - for ( ; upid >= pid->numbers; --upid) { > + for (upid = pid->numbers + ns->level; upid >= pid->numbers; --upid) { > /* Make the PID visible to find_pid_ns. */ > idr_replace(&upid->ns->idr, pid, upid->nr); > upid->ns->pid_allocated++; So.. unless I am totally confused the current code has another idr_preload + idr_preload_end around pidfs_add_pid(). AFAICS, this makes no sense, and your patch removes it. But perhaps this deserves a note in the changelog or even a separate patch? And another stupid question... I don't understand fs/pidfs.c, but it looks a bit strange to me that pidfs_add_pid() is called before the for (...) idr_replace(...); loop. I don't see any problem, but to me it would look a bit better to do pidfs_add_pid(pid) when this pid is fully initialized... Oleg.