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Thu, 16 Jan 2020 14:17:58 +0000 From: Tianyu Lan To: vkuznets , "lantianyu1986@gmail.com" CC: "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-mm@kvack.org" , "stable@vger.kernel.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "hpa@zytor.com" , "x86@kernel.org" , "dave.hansen@linux.intel.com" , "luto@kernel.org" , "peterz@infradead.org" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "sashal@kernel.org" , "akpm@linux-foundation.org" , Michael Kelley , Dexuan Cui Subject: RE: [EXTERNAL] Re: [PATCH] x86/Hyper-V: Balloon up according to request page number Thread-Topic: [EXTERNAL] Re: [PATCH] x86/Hyper-V: Balloon up according to request page number Thread-Index: AQHVyr1W8BxUjxrtnEuWgRAW3x4BfKftCkaQ Date: Thu, 16 Jan 2020 14:17:57 +0000 Message-ID: References: <20200114074435.12732-1-Tianyu.Lan@microsoft.com> <87blr6pepz.fsf@vitty.brq.redhat.com> In-Reply-To: <87blr6pepz.fsf@vitty.brq.redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=True; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 99571dd5-92e0-4418-8a58-08d79a8ee337 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Jan 2020 14:17:57.8849 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: KpwLnSVSF5H4w4S+ka/EV9ZIB6AdPksuiz7uK5psIZW/FE8IPPF0rtbIU9cCVuwNw+kA6YAiuigR9K0Bzuk0CQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PS1P15301MB0329 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org Hi Vitaly: Thanks for your review. I fix comments in V2.=20 > From: linux-hyperv-owner@vger.kernel.org owner@vger.kernel.org> On Behalf Of Vitaly Kuznetsov > Sent: Tuesday, January 14, 2020 5:31 PM > To: lantianyu1986@gmail.com > Cc: linux-kernel@vger.kernel.org; linux-hyperv@vger.kernel.org; linux- > mm@kvack.org; stable@vger.kernel.org; tglx@linutronix.de; > mingo@redhat.com; bp@alien8.de; hpa@zytor.com; x86@kernel.org; > dave.hansen@linux.intel.com; luto@kernel.org; peterz@infradead.org; KY > Srinivasan ; Haiyang Zhang ; > Stephen Hemminger ; sashal@kernel.org; > akpm@linux-foundation.org; Michael Kelley ; > Dexuan Cui > Subject: [EXTERNAL] Re: [PATCH] x86/Hyper-V: Balloon up according to requ= est > page number >=20 > lantianyu1986@gmail.com writes: >=20 > > From: Tianyu Lan > > > > Current code has assumption that balloon request memory size aligns > > with 2MB. But actually Hyper-V doesn't guarantee such alignment. When > > balloon driver receives non-aligned balloon request, it produces > > warning and balloon up more memory than requested in order to keep 2MB > alignment. > > Remove the warning and balloon up memory according to actual requested > > memory size. > > > > Fixes: f6712238471a ("hv: hv_balloon: avoid memory leak on alloc_error > > of 2MB memory block") > > Cc: stable@vger.kernel.org > > Signed-off-by: Tianyu Lan > > --- > > drivers/hv/hv_balloon.c | 7 ++----- > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index > > 7f3e7ab22d5d..38ad0e44e927 100644 > > --- a/drivers/hv/hv_balloon.c > > +++ b/drivers/hv/hv_balloon.c > > @@ -1684,7 +1684,7 @@ static unsigned int alloc_balloon_pages(struct > hv_dynmem_device *dm, > > if (num_pages < alloc_unit) > > return 0; > > > > - for (i =3D 0; (i * alloc_unit) < num_pages; i++) { > > + for (i =3D 0; i < num_pages / alloc_unit; i++) { > > if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) > > > HV_HYP_PAGE_SIZE) > > return i * alloc_unit; > > @@ -1722,7 +1722,7 @@ static unsigned int alloc_balloon_pages(struct > > hv_dynmem_device *dm, > > > > } > > > > - return num_pages; > > + return i * alloc_unit; > > } > > > > static void balloon_up(union dm_msg_info *msg_info) @@ -1737,9 > > +1737,6 @@ static void balloon_up(union dm_msg_info *msg_info) > > long avail_pages; > > unsigned long floor; > > > > - /* The host balloons pages in 2M granularity. */ > > - WARN_ON_ONCE(num_pages % PAGES_IN_2M !=3D 0); > > - > > /* > > * We will attempt 2M allocations. However, if we fail to > > * allocate 2M chunks, we will go back to PAGE_SIZE allocations. >=20 > This looks correct but I've noticed we also have >=20 > /* Refuse to balloon below the floor, keep the 2M granularity. */ > if (avail_pages < num_pages || avail_pages - num_pages < floor) { > pr_warn("Balloon request will be partially fulfilled. %s\n", > avail_pages < num_pages ? "Not enough memory." : > "Balloon floor reached."); >=20 > num_pages =3D avail_pages > floor ? (avail_pages - floor) : 0; > num_pages -=3D num_pages % PAGES_IN_2M; > } >=20 > in balloon_up(). If 2M granularity is not guaranteed in the first place w= e can't > keep it. >=20 > Also, when alloc_balloon_pages() is called with 2M alloc_unit and the reg= ion is > not 2M aligned, it will return someething < num_pages, the next condition= , > however, only checks for 0: >=20 > if (alloc_unit !=3D 1 && num_ballooned =3D=3D 0) { > alloc_unit =3D 1; > continue; > } >=20 > we will proceed to sending a response to server and try doing next iterat= ion by > calling alloc_balloon_pages() with 2M alloc_unit again, this will finally= return 0 > and we will switch to 4k. I think we can optimize this to: >=20 > if (alloc_unit !=3D 1 && num_ballooned !=3D num_pages) { > alloc_unit =3D 1; > continue; > } >=20 > -- > Vitaly