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dkim=pass header.d=fb.com header.s=facebook header.b=N+TKNmcZ; spf=pass (imf28.hostedemail.com: domain of "prvs=786498ca91=guro@fb.com" designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=786498ca91=guro@fb.com"; dmarc=pass (policy=reject) header.from=fb.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 841B090000B3 X-Stat-Signature: gq7f3mp6rkqwo7rp39nccttrh4eagqt7 X-HE-Tag: 1629252150-303949 Content-Transfer-Encoding: quoted-printable 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: On Mon, Aug 16, 2021 at 09:21:11PM +0800, Chen Huang wrote: >=20 >=20 > =E5=9C=A8 2021/8/16 16:34, Greg Kroah-Hartman =E5=86=99=E9=81=93: > > On Mon, Aug 16, 2021 at 07:21:37AM +0000, Chen Huang wrote: > >> From: Roman Gushchin > >=20 > > What is the git commit id of this patch in Linus's tree? > >=20 > >> > >> Patch series "mm: allow mapping accounted kernel pages to userspace"= , v6. > >> > >> Currently a non-slab kernel page which has been charged to a memory = cgroup > >> can't be mapped to userspace. The underlying reason is simple: Page= Kmemcg > >> flag is defined as a page type (like buddy, offline, etc), so it tak= es a > >> bit from a page->mapped counter. Pages with a type set can't be map= ped to > >> userspace. > >> > >> But in general the kmemcg flag has nothing to do with mapping to > >> userspace. It only means that the page has been accounted by the pa= ge > >> allocator, so it has to be properly uncharged on release. > >> > >> Some bpf maps are mapping the vmalloc-based memory to userspace, and= their > >> memory can't be accounted because of this implementation detail. > >> > >> This patchset removes this limitation by moving the PageKmemcg flag = into > >> one of the free bits of the page->mem_cgroup pointer. Also it forma= lizes > >> accesses to the page->mem_cgroup and page->obj_cgroups using new hel= pers, > >> adds several checks and removes a couple of obsolete functions. As = the > >> result the code became more robust with fewer open-coded bit tricks. > >> > >> This patch (of 4): > >> > >> Currently there are many open-coded reads of the page->mem_cgroup po= inter, > >> as well as a couple of read helpers, which are barely used. > >> > >> It creates an obstacle on a way to reuse some bits of the pointer fo= r > >> storing additional bits of information. In fact, we already do this= for > >> slab pages, where the last bit indicates that a pointer has an attac= hed > >> vector of objcg pointers instead of a regular memcg pointer. > >> > >> This commits uses 2 existing helpers and introduces a new helper to > >> converts all read sides to calls of these helpers: > >> struct mem_cgroup *page_memcg(struct page *page); > >> struct mem_cgroup *page_memcg_rcu(struct page *page); > >> struct mem_cgroup *page_memcg_check(struct page *page); > >> > >> page_memcg_check() is intended to be used in cases when the page can= be a > >> slab page and have a memcg pointer pointing at objcg vector. It doe= s > >> check the lowest bit, and if set, returns NULL. page_memcg() contai= ns a > >> VM_BUG_ON_PAGE() check for the page not being a slab page. > >> > >> To make sure nobody uses a direct access, struct page's > >> mem_cgroup/obj_cgroups is converted to unsigned long memcg_data. > >> > >> Signed-off-by: Roman Gushchin > >> Signed-off-by: Andrew Morton > >> Signed-off-by: Alexei Starovoitov > >> Reviewed-by: Shakeel Butt > >> Acked-by: Johannes Weiner > >> Acked-by: Michal Hocko > >> Link: https://lkml.kernel.org/r/20201027001657.3398190-1-guro@fb.com > >> Link: https://lkml.kernel.org/r/20201027001657.3398190-2-guro@fb.com > >> Link: https://lore.kernel.org/bpf/20201201215900.3569844-2-guro@fb.c= om > >> > >> Conflicts: > >> mm/memcontrol.c > >=20 > > The "Conflicts:" lines should be removed. > >=20 > > Please fix up the patch series and resubmit. But note, this seems > > really intrusive, are you sure these are all needed? > > Sorry for jumping in late. I agree that the patchset is quite intrusive and I really doubt we need to backport it. The main goal of my patchset was to enable memory accounting for bpf maps (which can be mmaped to userspace). I don't see why we need it otherwise. Muchun's patchset unifies the treatment of non-slab kernel objects (e.g. large kmallocs) with slab objects and prevents them to pin dying memory cgroups. However the problem existed for years and I doubt we need it in 5.10 so badly. >=20 > OK=EF=BC=8CI will resend the patchset. > Roman Gushchin's patchset formalize accesses to the page->mem_cgroup an= d > page->obj_cgroups. But for LRU pages and most other raw memcg, they may > pin to a memcg cgroup pointer, which should always point to an object c= group > pointer. That's the problem I met. And Muchun Song's patchset fix this. > So I think these are all needed. Can you, please, be more specific here? Thanks!