Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752715AbaKXH2W (ORCPT ); Mon, 24 Nov 2014 02:28:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33548 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752348AbaKXH2V (ORCPT ); Mon, 24 Nov 2014 02:28:21 -0500 Message-ID: <5472DE06.6000307@redhat.com> Date: Mon, 24 Nov 2014 15:28:06 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Dexuan Cui , "gregkh@linuxfoundation.org" , "linux-kernel@vger.kernel.org" , "driverdev-devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , KY Srinivasan CC: Haiyang Zhang Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on alloc_error of 2MB memory block References: <1416808575-5383-1-git-send-email-decui@microsoft.com> <5472BF95.2000904@redhat.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/24/2014 02:08 PM, Dexuan Cui wrote: >> -----Original Message----- >> > From: Jason Wang [mailto:jasowang@redhat.com] >> > Sent: Monday, November 24, 2014 13:18 PM >> > To: Dexuan Cui; gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org; >> > driverdev-devel@linuxdriverproject.org; olaf@aepfle.de; >> > apw@canonical.com; KY Srinivasan >> > Cc: Haiyang Zhang >> > Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on alloc_error of >> > 2MB memory block >> > >> > On 11/24/2014 01:56 PM, Dexuan Cui wrote: >>> > > If num_ballooned is not 0, we shouldn't neglect the already-allocated >> > 2MB >>> > > memory block(s). >>> > > >>> > > Cc: K. Y. Srinivasan >>> > > Cc: >>> > > Signed-off-by: Dexuan Cui >>> > > --- >>> > > drivers/hv/hv_balloon.c | 4 +++- >>> > > 1 file changed, 3 insertions(+), 1 deletion(-) >>> > > >>> > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c >>> > > index 5e90c5d..cba2d3b 100644 >>> > > --- a/drivers/hv/hv_balloon.c >>> > > +++ b/drivers/hv/hv_balloon.c >>> > > @@ -1091,6 +1091,8 @@ static void balloon_up(struct work_struct >> > *dummy) >>> > > bool done = false; >>> > > int i; >>> > > >>> > > + /* The host does balloon_up in 2MB. */ >>> > > + WARN_ON(num_pages % PAGES_IN_2M != 0); >>> > > >>> > > /* >>> > > * We will attempt 2M allocations. However, if we fail to >>> > > @@ -1111,7 +1113,7 @@ static void balloon_up(struct work_struct >> > *dummy) >>> > > bl_resp, alloc_unit, >>> > > &alloc_error); >>> > > >>> > > - if ((alloc_error) && (alloc_unit != 1)) { >>> > > + if (alloc_error && (alloc_unit != 1) && num_ballooned == 0) >> > { >>> > > alloc_unit = 1; >>> > > continue; >>> > > } >> > >> > Before the change, we may retry the 4K allocation when part or all 2M >> > allocations were failed. This makes sense when memory is fragmented. But > Yes, but all the partially-allocated 2MB memory blocks are lost(mem leak). > >> > after the change, if part of 2M allocation were failed, we won't retry >> > 4K allocation. Is this expected? > Hi Jason, > The patch doesn't break the "try 2MB first; then try 4K" logic: > > With the change, we'll retry the 2MB allocation in the next iteration of the > same while (!done) loop -- we expect this retry will cause > "alloc_error && (alloc_unit != 1) && num_ballooned == 0" to be true, > so we'll later try 4K allocation, as we did before. If I read the code correctly, if part of 2M allocation fails. alloc_balloon_pages() will have a non zero return value with alloc_error set. Then it will match the following check: if ((alloc_error) || (num_ballooned == num_pages)) { which will set done to true. So there's no second iteration of while (!done) loop? Probably you need something like: if ((alloc_unit != 1) && (num_ballooned == 0)) { alloc_unit = 1; continue; } if ((alloc_unit == 1) || (num_ballooned = num_pages)) { ... } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/