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[91.12.97.29]) by smtp.gmail.com with ESMTPSA id a4sm21295711wme.45.2021.06.09.03.56.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Jun 2021 03:56:01 -0700 (PDT) Subject: Re: [PATCH 7/9] docs: remove description of DISCONTIGMEM To: Mike Rapoport , Andrew Morton Cc: Arnd Bergmann , Geert Uytterhoeven , Ivan Kokshaysky , Jonathan Corbet , Matt Turner , Mike Rapoport , Richard Henderson , Vineet Gupta , kexec@lists.infradead.org, linux-alpha@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-xtensa@linux-xtensa.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org References: <20210602105348.13387-1-rppt@kernel.org> <20210602105348.13387-8-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat Message-ID: <6b92d273-dd0b-d67f-c2f6-cce13a33afd1@redhat.com> Date: Wed, 9 Jun 2021 12:56:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210602105348.13387-8-rppt@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 02.06.21 12:53, Mike Rapoport wrote: > From: Mike Rapoport > > Remove description of DISCONTIGMEM from the "Memory Models" document and > update VM sysctl description so that it won't mention DISCONIGMEM. > > Signed-off-by: Mike Rapoport > --- > Documentation/admin-guide/sysctl/vm.rst | 12 +++---- > Documentation/vm/memory-model.rst | 45 ++----------------------- > 2 files changed, 8 insertions(+), 49 deletions(-) > > diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst > index 586cd4b86428..ddbd71d592e0 100644 > --- a/Documentation/admin-guide/sysctl/vm.rst > +++ b/Documentation/admin-guide/sysctl/vm.rst > @@ -936,12 +936,12 @@ allocations, THP and hugetlbfs pages. > > To make it sensible with respect to the watermark_scale_factor > parameter, the unit is in fractions of 10,000. The default value of > -15,000 on !DISCONTIGMEM configurations means that up to 150% of the high > -watermark will be reclaimed in the event of a pageblock being mixed due > -to fragmentation. The level of reclaim is determined by the number of > -fragmentation events that occurred in the recent past. If this value is > -smaller than a pageblock then a pageblocks worth of pages will be reclaimed > -(e.g. 2MB on 64-bit x86). A boost factor of 0 will disable the feature. > +15,000 means that up to 150% of the high watermark will be reclaimed in the > +event of a pageblock being mixed due to fragmentation. The level of reclaim > +is determined by the number of fragmentation events that occurred in the > +recent past. If this value is smaller than a pageblock then a pageblocks > +worth of pages will be reclaimed (e.g. 2MB on 64-bit x86). A boost factor > +of 0 will disable the feature. > > > watermark_scale_factor > diff --git a/Documentation/vm/memory-model.rst b/Documentation/vm/memory-model.rst > index ce398a7dc6cd..30e8fbed6914 100644 > --- a/Documentation/vm/memory-model.rst > +++ b/Documentation/vm/memory-model.rst > @@ -14,15 +14,11 @@ for the CPU. Then there could be several contiguous ranges at > completely distinct addresses. And, don't forget about NUMA, where > different memory banks are attached to different CPUs. > > -Linux abstracts this diversity using one of the three memory models: > -FLATMEM, DISCONTIGMEM and SPARSEMEM. Each architecture defines what > +Linux abstracts this diversity using one of the two memory models: > +FLATMEM and SPARSEMEM. Each architecture defines what > memory models it supports, what the default memory model is and > whether it is possible to manually override that default. > > -.. note:: > - At time of this writing, DISCONTIGMEM is considered deprecated, > - although it is still in use by several architectures. > - > All the memory models track the status of physical page frames using > struct page arranged in one or more arrays. > > @@ -63,43 +59,6 @@ straightforward: `PFN - ARCH_PFN_OFFSET` is an index to the > The `ARCH_PFN_OFFSET` defines the first page frame number for > systems with physical memory starting at address different from 0. > > -DISCONTIGMEM > -============ > - > -The DISCONTIGMEM model treats the physical memory as a collection of > -`nodes` similarly to how Linux NUMA support does. For each node Linux > -constructs an independent memory management subsystem represented by > -`struct pglist_data` (or `pg_data_t` for short). Among other > -things, `pg_data_t` holds the `node_mem_map` array that maps > -physical pages belonging to that node. The `node_start_pfn` field of > -`pg_data_t` is the number of the first page frame belonging to that > -node. > - > -The architecture setup code should call :c:func:`free_area_init_node` for > -each node in the system to initialize the `pg_data_t` object and its > -`node_mem_map`. > - > -Every `node_mem_map` behaves exactly as FLATMEM's `mem_map` - > -every physical page frame in a node has a `struct page` entry in the > -`node_mem_map` array. When DISCONTIGMEM is enabled, a portion of the > -`flags` field of the `struct page` encodes the node number of the > -node hosting that page. > - > -The conversion between a PFN and the `struct page` in the > -DISCONTIGMEM model became slightly more complex as it has to determine > -which node hosts the physical page and which `pg_data_t` object > -holds the `struct page`. > - > -Architectures that support DISCONTIGMEM provide :c:func:`pfn_to_nid` > -to convert PFN to the node number. The opposite conversion helper > -:c:func:`page_to_nid` is generic as it uses the node number encoded in > -page->flags. > - > -Once the node number is known, the PFN can be used to index > -appropriate `node_mem_map` array to access the `struct page` and > -the offset of the `struct page` from the `node_mem_map` plus > -`node_start_pfn` is the PFN of that page. > - > SPARSEMEM > ========= > > Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb