From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 98602 invoked by alias); 8 Aug 2019 18:21:34 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 98588 invoked by uid 89); 8 Aug 2019 18:21:33 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-17.8 required=5.0 tests=AWL,BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 spammy= X-HELO: mail-qk1-f196.google.com Return-Path: Subject: Re: [PATCH] malloc: Fix missing accounting of top chunk in malloc_info [BZ #24026] To: Florian Weimer Cc: libc-alpha@sourceware.org, =?UTF-8?Q?Niklas_Hamb=c3=bcchen?= References: <87blx9hyo7.fsf@oldenburg2.str.redhat.com> <87ftmkhmg2.fsf@oldenburg2.str.redhat.com> <757d8c19-6f15-928c-1adf-d818d0347e7f@redhat.com> <87h86tf3tf.fsf@oldenburg2.str.redhat.com> From: Carlos O'Donell Message-ID: <9079797d-c7ca-a521-f2a0-d53e33c225e9@redhat.com> Date: Thu, 08 Aug 2019 18:21:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <87h86tf3tf.fsf@oldenburg2.str.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-SW-Source: 2019-08/txt/msg00147.txt.bz2 On 8/7/19 10:27 AM, Florian Weimer wrote: > * Carlos O'Donell: > >> I agree with you that this looks correct, but I would >> really have expected the top chunk to be in one of >> the counted bins if it was actually free. However, it >> turns out I'm wrong. The code and logic treat top >> as a chunk which is no bin. And even when we expand >> the heap we have to manually free the old top, and only >> at that point does it enter into a bin, because the new >> top on the new heap is now the special top. >> >> Please repost with a comment to that effect added: >> >> /* The top-most available chunk is treated specially >> and is never in any bin. See "initial_top" comments. */ > > Please see below. LGTM. Reviewed-by: Carlos O'Donell > Thanks, > Florian > > From: Niklas Hambüchen > Subject: malloc: Fix missing accounting of top chunk in malloc_info [BZ #24026] > > Fixes ` incorrectly showing as 0 most > of the time. > > The rest value being wrong is significant because to compute the > actual amount of memory handed out via malloc, the user must subtract > it from . That result being wrong > makes investigating memory fragmentation issues like > close to > impossible. > > 2019-08-07 Niklas Hambüchen > Carlos O'Donell > > [BZ #24026] > * malloc/malloc.c (__malloc_info): Account for top chunk. > > diff --git a/malloc/malloc.c b/malloc/malloc.c > index 343d89f489..0e65d636cd 100644 > --- a/malloc/malloc.c > +++ b/malloc/malloc.c > @@ -5406,6 +5406,12 @@ __malloc_info (int options, FILE *fp) > > __libc_lock_lock (ar_ptr->mutex); > > + /* Account for top chunk. The top-most available chunk is > + treated specially and is never in any bin. See "initial_top" > + comments. */ > + avail = chunksize (ar_ptr->top); > + nblocks = 1; /* Top always exists. */ > + > for (size_t i = 0; i < NFASTBINS; ++i) > { > mchunkptr p = fastbin (ar_ptr, i); > -- Cheers, Carlos.