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Thu, 10 Sep 2020 13:27:47 -0700 Received: from intmgw002.06.prn3.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:11d::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Thu, 10 Sep 2020 13:27:09 -0700 Received: by devvm1096.prn0.facebook.com (Postfix, from userid 111017) id BB3623D449B8; Thu, 10 Sep 2020 13:27:03 -0700 (PDT) Smtp-Origin-Hostprefix: devvm From: Roman Gushchin Smtp-Origin-Hostname: devvm1096.prn0.facebook.com To: Andrew Morton , CC: =Shakeel Butt , Johannes Weiner , Michal Hocko , , , Roman Gushchin Smtp-Origin-Cluster: prn0c01 Subject: [PATCH rfc 4/5] mm: introduce page memcg flags Date: Thu, 10 Sep 2020 13:26:58 -0700 Message-ID: <20200910202659.1378404-5-guro@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200910202659.1378404-1-guro@fb.com> References: <20200910202659.1378404-1-guro@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-10_09:2020-09-10,2020-09-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 clxscore=1015 adultscore=0 impostorscore=0 spamscore=0 malwarescore=0 bulkscore=0 mlxlogscore=317 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009100184 X-FB-Internal: deliver X-Rspamd-Queue-Id: CE5FA180AD817 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: The lowest bit in page->memcg_data is used to distinguish between struct memory_cgroup pointer and a pointer to a objcgs array. All checks and modifications of this bit are open-coded. Let's formalize it using page memcg flags, defined in page_memcg_flags enum and replace all open-coded accesses with test_bit()/__set_bit(). Few additional flags might be added later. Flags are intended to be mutually exclusive. Signed-off-by: Roman Gushchin --- include/linux/memcontrol.h | 34 +++++++++++++++++++++++----------- 1 file changed, 23 insertions(+), 11 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 48d4c2c1ce81..7ab5f92bb686 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -340,23 +340,25 @@ struct mem_cgroup { =20 extern struct mem_cgroup *root_mem_cgroup; =20 +enum page_memcg_flags { + /* page->memcg_data is a pointer to a objcgs vector */ + PG_MEMCG_OBJ_CGROUPS, +}; + static inline struct mem_cgroup *page_mem_cgroup(struct page *page) { + unsigned long memcg_data =3D page->memcg_data; + VM_BUG_ON_PAGE(PageSlab(page), page); - return (struct mem_cgroup *)page->memcg_data; + + return (struct mem_cgroup *)memcg_data; } =20 static inline struct mem_cgroup *page_mem_cgroup_check(struct page *page= ) { unsigned long memcg_data =3D page->memcg_data; =20 - /* - * The lowest bit set means that memcg isn't a valid - * memcg pointer, but a obj_cgroups pointer. - * In this case the page is shared and doesn't belong - * to any specific memory cgroup. - */ - if (memcg_data & 0x1UL) + if (test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data)) return NULL; =20 return (struct mem_cgroup *)memcg_data; @@ -378,14 +380,20 @@ static inline void clear_page_mem_cgroup(struct pag= e *page) #ifdef CONFIG_MEMCG_KMEM static inline struct obj_cgroup **page_obj_cgroups(struct page *page) { - return (struct obj_cgroup **)(page->memcg_data & ~0x1UL); + unsigned long memcg_data =3D page->memcg_data; + + VM_BUG_ON_PAGE(memcg_data && !test_bit(PG_MEMCG_OBJ_CGROUPS, + &memcg_data), page); + __clear_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data); + + return (struct obj_cgroup **)memcg_data; } =20 static inline struct obj_cgroup **page_obj_cgroups_check(struct page *pa= ge) { unsigned long memcg_data =3D page->memcg_data; =20 - if (memcg_data && (memcg_data & 0x1UL)) + if (memcg_data && test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data)) return (struct obj_cgroup **)memcg_data; =20 return NULL; @@ -394,7 +402,11 @@ static inline struct obj_cgroup **page_obj_cgroups_c= heck(struct page *page) static inline bool set_page_obj_cgroups(struct page *page, struct obj_cgroup **objcgs) { - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL); + unsigned long memcg_data =3D (unsigned long)objcgs; + + __set_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data); + + return !cmpxchg(&page->memcg_data, 0, memcg_data); } =20 static inline void clear_page_obj_cgroups(struct page *page) --=20 2.26.2