처음으로 | 찾기 | 아카이브 | 글 올리기 | 링크 | 자료실 | 통계 | 연락처 | 자유게시판
이지도움 특집
TI DaVinci
Analog Blackfin
캐쉬의 모든것
메모리 할당 알고리즘
CPU 파이프라이닝




사용자 등록

현재 접속중인 등록 사용자는 0명, 익명 사용자는 1명 입니다.
전체 등록 사용자: 751명

마지막 답장
·libcurl + fuse 조합으로 되는게 많네. (1)
·Linux Ftrace에 관해 (3)
·Android MTP ( Media Transfer Protocol ) (1)
·Lighttpd에 인증을 digest 사용시 IE 오동작 문제? (1)
·Dtrace에 관해 (1)

·OpenSSL and multi-threads (0)
·ARM 환경에서 OpenCL 사용 (0)
·IoT용 WIFI 모듈 비교 ( MCU ) 클래스 (0)
·Glances - 리눅스 여러 가지 항목을 한 화면에서 모니터링 (0)
·plugin 방식의 로그 분석기 (0)

뜨거운 감자
·나는 인터렉티브한 환경에서 역어셈블 한다. (12)
·GNU REGEX (정규표현식) 프로그래밍 강좌 (7)
·SoCRobotWar 2005 - 신입생 기초 교육자료 (7)
·ASP.NET의 데이터 그리드와 사용자 컨트롤 (7)
·DHTML Editing Control (7)

가장 많이 읽은 글
·[Cache] 2-way Set-Associative 방식이란 무엇일까? (2)
·멀티쓰레드(Pthread) 프로그래밍
·Sorting Algorithm Animation (2)
·GNU REGEX (정규표현식) 프로그래밍 강좌 (7)
·SoCRobotWar 2005 - 신입생 기초 교육자료 (7)

Zone balancing
글쓴이: EzDoum 글쓴날: 2002년 05월 02일 오전 03:49

커널 버젼 2.2.X 하고 2.4.X하고 mm/page_alloc.c 가 상당히
다르네요. Zone balancing란 녀석이 도입이
된듯한데.... 암튼 더 찾아봐야할듯,..

아래의 문서는 커널 Documentation/vm/balance 문서입니다.

Started Jan 2000 by Kanoj Sarcar

Memory balancing is needed for non __GFP_WAIT as well as for non
__GFP_IO allocations.

There are two reasons to be requesting non __GFP_WAIT allocations:
the caller can not sleep (typically intr context), or does not want
to incur cost overheads of page stealing and possible swap io for
whatever reasons.

__GFP_IO allocation requests are made to prevent file system deadlocks.

In the absence of non sleepable allocation requests, it seems detrimental
to be doing balancing. Page reclamation can be kicked off lazily, that
is, only when needed (aka zone free memory is 0), instead of making it
a proactive process.

That being said, the kernel should try to fulfill requests for direct
mapped pages from the direct mapped pool, instead of falling back on
the dma pool, so as to keep the dma pool filled for dma requests (atomic
or not). A similar argument applies to highmem and direct mapped pages.
OTOH, if there is a lot of free dma pages, it is preferable to satisfy
regular memory requests by allocating one from the dma pool, instead
of incurring the overhead of regular zone balancing.

In 2.2, memory balancing/page reclamation would kick off only when the
_total_ number of free pages fell below 1/64 th of total memory. With the
right ratio of dma and regular memory, it is quite possible that balancing
would not be done even when the dma zone was completely empty. 2.2 has
been running production machines of varying memory sizes, and seems to be
doing fine even with the presence of this problem. In 2.3, due to
HIGHMEM, this problem is aggravated.

In 2.3, zone balancing can be done in one of two ways: depending on the
zone size (and possibly of the size of lower class zones), we can decide
at init time how many free pages we should aim for while balancing any
zone. The good part is, while balancing, we do not need to look at sizes
of lower class zones, the bad part is, we might do too frequent balancing
due to ignoring possibly lower usage in the lower class zones. Also,
with a slight change in the allocation routine, it is possible to reduce
the memclass() macro to be a simple equality.

Another possible solution is that we balance only when the free memory
of a zone _and_ all its lower class zones falls below 1/64th of the
total memory in the zone and its lower class zones. This fixes the 2.2
balancing problem, and stays as close to 2.2 behavior as possible. Also,
the balancing algorithm works the same way on the various architectures,
which have different numbers and types of zones. If we wanted to get
fancy, we could assign different weights to free pages in different
zones in the future.

Note that if the size of the regular zone is huge compared to dma zone,
it becomes less significant to consider the free dma pages while
deciding whether to balance the regular zone. The first solution
becomes more attractive then.

The appended patch implements the second solution. It also "fixes" two
problems: first, kswapd is woken up as in 2.2 on low memory conditions
for non-sleepable allocations. Second, the HIGHMEM zone is also balanced,
so as to give a fighting chance for replace_with_highmem() to get a
HIGHMEM page, as well as to ensure that HIGHMEM allocations do not
fall back into regular zone. This also makes sure that HIGHMEM pages
are not leaked (for example, in situations where a HIGHMEM page is in
the swapcache but is not being used by anyone)

kswapd also needs to know about the zones it should balance. kswapd is
primarily needed in a situation where balancing can not be done,
probably because all allocation requests are coming from intr context
and all process contexts are sleeping. For 2.3, kswapd does not really
need to balance the highmem zone, since intr context does not request
highmem pages. kswapd looks at the zone_wake_kswapd field in the zone
structure to decide whether a zone needs balancing.

Page stealing from process memory and shm is done if stealing the page would
alleviate memory pressure on any zone in the page's node that has fallen below
its watermark.

pages_min/pages_low/pages_high/low_on_memory/zone_wake_kswapd: These are
per-zone fields, used to determine when a zone needs to be balanced. When
the number of pages falls below pages_min, the hysteric field low_on_memory
gets set. This stays set till the number of free pages becomes pages_high.
When low_on_memory is set, page allocation requests will try to free some
pages in the zone (providing GFP_WAIT is set in the request). Orthogonal
to this, is the decision to poke kswapd to free some zone pages. That
decision is not hysteresis based, and is done when the number of free
pages is below pages_low; in which case zone_wake_kswapd is also set.

(Good) Ideas that I have heard:
1. Dynamic experience should influence balancing: number of failed requests
for a zone can be tracked and fed into the balancing scheme (jalvo@mbay.net)
2. Implement a replace_with_highmem()-like replace_with_regular() to preserve
dma pages. (lkd@tantalophile.demon.co.uk)

  • 관련 링크
  • [분류: 리눅스 커널 인쇄용 페이지 본문 email로 보내기 ]

    <  카르노 맵(Karnaugh map) | 리눅스 메모리 관리의 이해를 돕는 그림들  >

    답장 쓰기
    글을 올리시려면 로그인 (사용자 등록) 하셔야 합니다.


    ·공지 (6)
    ·인터넷 (87)
    ·하드웨어 (260)
    ·C/C++ (65)
    ·어셈블리 (7)
    ·리눅스 (136)
    ·리눅스 커널 (67)
    ·윈도우즈 (25)
    ·데이터베이스 (20)
    ·보안 (16)
    ·.NET (25)
    ·그래픽 (13)
    ·책소개 (42)
    ·호기심 천국 (80)
    ·잡담 (111)
    ·사랑 (3)

    전체 본문수: 963
    전체 답장수: 525

    분류 : 리눅스 커널
    가장 많이 읽은 글
    ·리눅스 커널 공부하기 (2)
    뜨거운 감자
    ·SunWorld Online (4)

    이지도움 어때요?
    이게 뭐야. 다시 안올란다. --;
    아이 좋아라~ +_+;
    먼가는 있는거 같은데 뭐하는 곳이지?
    기타 (자유게시판에 글로 남겨 주세요)
    [ 결과 | 투표 ]

    랜덤 링크

     Home ^ BACK TO TOP ^ EzDoum - 도움이 필요하세요~??
     Powered by KorWeblog 1.5.8 Copyleft © 2001 EzDoum, 관리자: EzDoum