Lines Matching +full:data +full:- +full:mapping

18 The part of (physical) memory not covered by a permanent mapping is what we
30 		+--------+ 0xffffffff
32 		+--------+ 0xc0000000
36 		+--------+ 0x00000000
39 time, but because we need virtual address space for other things - including
40 temporary maps to access the rest of the physical memory - the actual direct
54 * kmap_local_page(), kmap_local_folio() - These functions are used to create
64   These mappings are thread-local and CPU-local, meaning that the mapping
66   CPU while the mapping is active. Although preemption is never disabled by
68   CPU-hotplug until the mapping is disposed.
71   in which the local mapping is acquired does not allow it for other reasons.
82   virtual address of the direct mapping. Only real highmem pages are
95   therefore try to design their code to avoid the use of kmap() by mapping
107   NOTE: Conversions to kmap_local_page() must take care to follow the mapping
116   This permits a very short duration mapping of a single page.  Since the
117   mapping is restricted to the CPU that issued it, it performs well, but
125   Each call of kmap_atomic() in the kernel creates a non-preemptible section
133   NOTE: Conversions to kmap_local_page() must take care to follow the mapping
140   This should be used to make short duration mapping of a single page with no
141   restrictions on preemption or migration. It comes with an overhead as mapping
143   mapping is no longer needed, the address that the page was mapped to must be
146   Mapping changes must be propagated across all the CPUs. kmap() also
148   block when the mapping space is fully utilized until a slot becomes
151   All the above work is necessary if a mapping must last for a relatively
152   long time but the bulk of high-memory mappings in the kernel are
153   short-lived and only used in one place. This means that the cost of
159   On 64-bit systems, calls to kmap_local_page(), kmap_atomic() and kmap() have
160   no real work to do because a 64-bit address space is more than sufficient to
163 * vmap().  This can be used to make a long duration mapping of multiple
172 manipulate the kernel's page tables, the data TLB and/or the MMU's registers.
174 If CONFIG_HIGHMEM is not set, then the kernel will try and create a mapping
187 of RAM into your 32-bit machine.  This has a number of consequences:
189 * Linux needs a page-frame structure for each page in the system and the
190   pageframes need to live in the permanent mapping, which means:
192 * you can have 896M/sizeof(struct page) page-frames at most; with struct
193   page being 32-bytes that would end up being something in the order of 112G
195   page-frames in that memory...
197 * PAE makes your page tables larger - which slows the system down as more
198   data has to be accessed to traverse in TLB fills and the like.  One
202 The general recommendation is that you don't use more than 8GiB on a 32-bit
203 machine - although more might work for you and your workload, you're pretty
204 much on your own - don't expect kernel developers to really care much if things
211 .. kernel-doc:: include/linux/highmem.h
212 .. kernel-doc:: mm/highmem.c
213 .. kernel-doc:: include/linux/highmem-internal.h