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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6607EC433FE for ; Fri, 22 Apr 2022 12:28:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1447487AbiDVMa7 (ORCPT ); Fri, 22 Apr 2022 08:30:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230061AbiDVMa6 (ORCPT ); Fri, 22 Apr 2022 08:30:58 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6806056C27; Fri, 22 Apr 2022 05:28:05 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 0F6FC1F745; Fri, 22 Apr 2022 12:28:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1650630484; 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=NFjKDOpABJHRIxw0TYxlJyyUYk2rVUx2NABXdGw59hw=; b=eU+jKeekea5RxUZW6HIGzmrZC40OwawfZ3nKfEqK7FH/3dj9Sz+68uCxba2WFY+ULD/oPH KlhAFBKDTe+13b9sHBqxXNmknfWppxSfzXutPvXO9p3+Qc4TgRxXPpVlOOjFv77Wmz9z96 xt5a51+F5BQOAlvQfmmtvCe2xb+etA8= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id CD12A2C141; Fri, 22 Apr 2022 12:28:03 +0000 (UTC) Date: Fri, 22 Apr 2022 14:28:03 +0200 From: Michal Hocko To: Kent Overstreet Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hch@lst.de, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org, linux-input@vger.kernel.org, roman.gushchin@linux.dev Subject: Re: [PATCH v2 3/8] mm/memcontrol.c: Convert to printbuf Message-ID: References: <20220421234837.3629927-1-kent.overstreet@gmail.com> <20220421234837.3629927-9-kent.overstreet@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220421234837.3629927-9-kent.overstreet@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On Thu 21-04-22 19:48:32, Kent Overstreet wrote: > This converts memory_stat_format() from seq_buf to printbuf. Printbuf is > simalar to seq_buf except that it heap allocates the string buffer: > here, we were already heap allocating the buffer with kmalloc() so the > conversion is trivial. What is the advantage of changing a well tested seq_buf with a different way to do the same thing here? I do not see this to be a noticeable simplification of the existing code. The only advantage I can see is that the string storage allocation is implicit and it would expand in case we ever overflow over a single page. But is this really worth the code churn? > Signed-off-by: Kent Overstreet > --- > mm/memcontrol.c | 68 ++++++++++++++++++++++++------------------------- > 1 file changed, 33 insertions(+), 35 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 36e9f38c91..4cb0b7bc1c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -61,7 +61,7 @@ > #include > #include > #include > -#include > +#include > #include "internal.h" > #include > #include > @@ -1436,13 +1436,9 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg, > > static char *memory_stat_format(struct mem_cgroup *memcg) > { > - struct seq_buf s; > + struct printbuf buf = PRINTBUF; > int i; > > - seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE); > - if (!s.buffer) > - return NULL; > - > /* > * Provide statistics on the state of the memory subsystem as > * well as cumulative event counters that show past behavior. > @@ -1459,49 +1455,51 @@ static char *memory_stat_format(struct mem_cgroup *memcg) > u64 size; > > size = memcg_page_state_output(memcg, memory_stats[i].idx); > - seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size); > + pr_buf(&buf, "%s %llu\n", memory_stats[i].name, size); > > if (unlikely(memory_stats[i].idx == NR_SLAB_UNRECLAIMABLE_B)) { > size += memcg_page_state_output(memcg, > NR_SLAB_RECLAIMABLE_B); > - seq_buf_printf(&s, "slab %llu\n", size); > + pr_buf(&buf, "slab %llu\n", size); > } > } > > /* Accumulated memory events */ > > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGFAULT), > - memcg_events(memcg, PGFAULT)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGMAJFAULT), > - memcg_events(memcg, PGMAJFAULT)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGREFILL), > - memcg_events(memcg, PGREFILL)); > - seq_buf_printf(&s, "pgscan %lu\n", > - memcg_events(memcg, PGSCAN_KSWAPD) + > - memcg_events(memcg, PGSCAN_DIRECT)); > - seq_buf_printf(&s, "pgsteal %lu\n", > - memcg_events(memcg, PGSTEAL_KSWAPD) + > - memcg_events(memcg, PGSTEAL_DIRECT)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGACTIVATE), > - memcg_events(memcg, PGACTIVATE)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGDEACTIVATE), > - memcg_events(memcg, PGDEACTIVATE)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGLAZYFREE), > - memcg_events(memcg, PGLAZYFREE)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGLAZYFREED), > - memcg_events(memcg, PGLAZYFREED)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGFAULT), > + memcg_events(memcg, PGFAULT)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGMAJFAULT), > + memcg_events(memcg, PGMAJFAULT)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGREFILL), > + memcg_events(memcg, PGREFILL)); > + pr_buf(&buf, "pgscan %lu\n", > + memcg_events(memcg, PGSCAN_KSWAPD) + > + memcg_events(memcg, PGSCAN_DIRECT)); > + pr_buf(&buf, "pgsteal %lu\n", > + memcg_events(memcg, PGSTEAL_KSWAPD) + > + memcg_events(memcg, PGSTEAL_DIRECT)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGACTIVATE), > + memcg_events(memcg, PGACTIVATE)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGDEACTIVATE), > + memcg_events(memcg, PGDEACTIVATE)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGLAZYFREE), > + memcg_events(memcg, PGLAZYFREE)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(PGLAZYFREED), > + memcg_events(memcg, PGLAZYFREED)); > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(THP_FAULT_ALLOC), > - memcg_events(memcg, THP_FAULT_ALLOC)); > - seq_buf_printf(&s, "%s %lu\n", vm_event_name(THP_COLLAPSE_ALLOC), > - memcg_events(memcg, THP_COLLAPSE_ALLOC)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(THP_FAULT_ALLOC), > + memcg_events(memcg, THP_FAULT_ALLOC)); > + pr_buf(&buf, "%s %lu\n", vm_event_name(THP_COLLAPSE_ALLOC), > + memcg_events(memcg, THP_COLLAPSE_ALLOC)); > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > - /* The above should easily fit into one page */ > - WARN_ON_ONCE(seq_buf_has_overflowed(&s)); > + if (buf.allocation_failure) { > + printbuf_exit(&buf); > + return NULL; > + } > > - return s.buffer; > + return buf.buf; > } > > #define K(x) ((x) << (PAGE_SHIFT-10)) > -- > 2.35.2 -- Michal Hocko SUSE Labs