--- #NGUYEN THANH NAM# <[EMAIL PROTECTED]> wrote:
> HIGHMEM la` memory tu+` 4GB tro+? le^n.
Highmem tro? to+'i vu`ng nho+' tu+` 1GB tro+? ra,
chu+' kho^ng pha?i 4G.
Nguye^n nha^n co' "highmem" la` vi` tre^n x86
architecture (32 bit), kho^ng gian vu`ng nho+' a?o
gio+'i ha.n trong khoa?ng 4GB. (Vanilla) kernel chia
vu`ng na`y la`m 2 khu'c: tu+` 0->3GB-1 cho u+'ng du.ng
(go.i la` userspace) va` 3GB->4GB cho kernel (go.i la`
kernelspace). Kernel se~ a'nh xa. (map) vu`ng nho+'
va^.t ly' (physical memory), va` do khu'c da`nh cho
kernel chi? la` 1GB ne^n ta.i mo^.t tho+`i ddie^?m
kernel chi? co' the^? truy nha^.p (permanently mapped)
1GB bo^. nho+'. Vi` nguye^n nha^n na`y ne^'u ma'y co'
tre^n 1GB memory, kernel se~ pha?i su+? du.ng 1 co+
che^' dda(.c bie^.t dde^? truy nha^.p vu`ng nho+'
ngoa`i pha.m vi 1GB na`y\. Vu`ng na`y ddu+o+.c go.i
la` HIGHMEM (ddu+o+.c ddi.nh nghi~a nhu+ la`
ZONE_HIGHMEM, tra'i vo+'i ZONE_NORMAL la` vu`ng nho+'
tu+` 0->1GB).
Ky~ thua^.t map highmem va`o vu`ng nho+' thu+o+`ng
(ZONE_NORMAL) ho+i tricky va` co' hie^.u na(ng su+?
du.ng ke'm xa so vo+'i khi su+? du.ng vu`ng nho+'
thu+o+`ng.
Thu? thua^.t du`ng dde^? truy ca^.p highmem chi? su+?
du.ng vo+'i ca'c platform 32 bit. Vo+'i ca'c 64bit
architecture (nhu+ AMD Opteron), highmem kho^ng co`n
ca^`n thie^'t nu+~a\.
> BIOS-e820: 00000000fff00000 - 0000000100000000
(reserved)
> 0MB HIGHMEM available.
Ca'i do`ng tre^n kho^ng lie^n quan gi` to+'i do`ng
du+o+'i ca?. Do`ng tre^n tho^ng ba'o he^. tho^'ng khi
kho+?i ddo^.ng dda~ da`nh rie^ng ra mo^.t bo^. pha^.n
vu`ng nho+' va` kho^ng ddu+o+.c su+? du.ng vu`ng na`y.
Do`ng du+o+'i co' the^? hie^?u la` ma'y cu. maikhai
kho^ng co' highmem - tu+'c la` kho^ng co' tre^n 1GB
va`/hoa(.c su+? du.ng kernel kho^ng ho^~ tro+. bo^.
nho+' tre^n 1GB (xem the^m cho.n lu+.a "High memory
support" khi bie^n di.ch kernel)
Tuy nhie^n ne^'u thi'ch cu. co' the^? patch kernel
dde^? co' highmem - du`ng khi debug highmem trong
tru+o+`ng ho+.p ma'y kho^ng co' to+'i 1GB memory,
hoa(.c khi cu. thi'ch nghi.ch ;-)
0xdeface
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