[PDF] Page Segmentation Using Convolutional Neural Network and - Spr





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Gestion de la mémoire

Allocation d'espace pour l'accroissement de la pile et d'un segment de données. Modèle de mémoire fusionné (mélange de pagination et segmentation).



Systèmes dExploitation - Gestion de la mémoire

contigüe. Monoprogrammation. Multiprogrammation. Pagination. Segmentation. Systèmes d'Exploitation. Gestion de la mémoire. Didier Verna didier@lrde.epita.fr.



Module 7 Gestion de la mémoire

Partitions dynamiques: fragmentation externe qui conduit au besoin de compression. ?. Segmentation sans pagination: pas de fragmentation interne mais 



Smart card introduction

La segmentation est visible au programmeur mais la pagination ne l'est pas. • Le segment est une unité logique de protection et partage tandis que la page ne l 



Chapitre 4

Programmation du Noyau Linux. Olivier Dalle. Mémoire. Translation d'adresses. Unité de Segmentation. Unité de Pagination. Programme. Adresse Logique.



La gestion de la mémoire

segmentation de l'espace d'adressage des programmes pour les raisons suivantes La pagination consiste à diviser la mémoire et les processus en blocs de ...



Gestion de la mémoire

En combinant segmentation et pagination. MULTICS combine les avantages des deux techniques en s'affranchissant des principaux défauts qu'ils ont : fragmentation 



La gestion de la mémoire

? la segmentation : les programmes sont découpés en parcelles ayant des longueurs variables appelées. «segments». ? la pagination : elle consiste à diviser la 





1. Segmentation 2. Pagination

Segmentation. On considère la table des segments suivante pour un processus P1 : Index Base Limite Calculez les adresses physiques correspondant aux 



Page Segmentation using Visual Adjacency Analysis - arXivorg

Page segmentation is a web page analysis process that divides a page into cohesive segments such as sidebars headers and footers Current page segmentation approaches use either the DOM textual content or rendering style information of the page However these approaches have a number of drawbacks such as a large number of



Page Segmentation Using Convolutional Neural Network and - Spr

Paging Segmentation Page size Page size is de?ned by the hardware Often of the form 2n between 512 bytes and 16 MB typically 4-8 KB page number page offset p d m ?n n Must be carefully chosen: too large means more internal fragmentation too small means too much overhead in paging management and processing



W4118: segmentation and paging - Department of Computer

Implementation of page table Page table is stored in memory Page table base register (PTBR) points to the base of page table • x86: cr3 OS stores base in process control block (PCB) OS switches PTBR on each context switch Problem: each data/instruction access requires two memory accesses Extra memory access for page table 21

What is page segmentation?

It is aimed at segmenting the entire document images into small regions with homogeneous contents and high level semantics such as paragraphs, titles, lists, tables and figures. Page segmentation is a prerequisite for many following applications such as text line transcription, table structure analysis and figure classification, etc.

How effective is page segmentation using convolutional neural network and graphical model?

In this paper, we propose an effective method for page segmentation using convolutional neural network (CNN) and graphical model, where the CNN is powerful for extracting visual features and the graphical model explores the relationship (spatial context) between visual primitives and regions.

What are the advantages of paging a segment?

Given to segmentation unit Linear address given to paging unit Check: permissions Segment sharing Easier to relocate segment than entire program Avoids allocating unused memory Flexible protection Efficient translation Segments have variable lengths how to fit? Eliminate fragmentation due to large segments

What are the principles of segmentation?

Segmentation A. Divide an object into independent parts. B. Make an object easy to disassemble. C. Increase the degree of fragmentation or segmentation. Principle 2. Taking out A. Separate an interfering part or property from an object, or single out the only necessary part. Principle 3.

Paging & Segmentation

Frédéric Haziza

Department of Computer Systems

Uppsala University

Spring 2007

PagingSegmentation

Outline

1Paging

Implementation

Protection

Sharing

2Segmentation

Setup

Implementation

PagingSegmentation

Definition

Paging

Memory-management technique that permits the physical address space of a process to be non-contiguous

Avoids external fragmentation

PagingSegmentation

Basics

New setup:

Physical memoryis divided intoframes

Logical memoryis divided intopages

A frame

has the same size as a page is a place where a (logical) page can be (physically) placed

PagingSegmentation

Logical to Physical

Translation

Logical address space→page table per process→physical address space

Page 0

Page 1

Page 2

Page 3

Logical memory

01 14 23
37

Page table

↓Frame number 0

1Page 0

2

3Page 2

4Page 1

5 6

7Page 3

Physical memory

Note: Similar torelocation register per page

PagingSegmentation

How does it work?

See black board...

...take your notes...

PagingSegmentation

Page size

Page size is defined by the hardware.

Often of the form 2n, between 512 bytes and 16 MB, typically 4-8 KB page number page offset pd m-nn Must be carefully chosen: too large means more internal fragmentation, too small means too much overhead in paging management and processing.

If page table entry = 4 byte (= 32 bits), 2

32page frames.

If page frame = 4 KB?can address 244bytes (=16 TB) of physycial memory.

PagingSegmentation

Characteristics

The current page table (address) is saved and restored when doing a context switch.

The OS also has a

frame tablecontaining information about all frames, e.g. whether they are free or which process(es) is/are using it

PagingSegmentation

Characteristics

No external fragmentation

all frames (physical memory) can be used by processes

Possible internal fragmentation

on average 1/2 page per process (the last page) The physical memoryused by a processis no longer contiguous The logical memory of a process is still contiguous

The logical and physical addresses are separated

the process does not see the translation or the difference tohaving physical memory

PagingSegmentation

Implementation

Implementation must be done in hardware for efficiency. All process address references go through address translation: memory not allocated to the process can not be touched by the processes.

PagingSegmentation

Small page tables

Example (PDP-11)

16-bit addresses with 8 KB page size

?8 pages kept in dedicated registers, updated (like all registers) at context switch.

PagingSegmentation

Larger page tables

Modern systems can have millions of pages.

?Move the page table to main memory, addressed by Page

Table Base Register

(PTBR) which is updated at context switch. Problem: Each logical memory reference generates two physical references (one for page table, one for real access).

Solution: Can we remember one maybe?

Translation Look-aside Buffer (TLB): fast cache with associative memory.(Keeps only recently used Page Table entries) Associative memory looks up the key(page number)in parallel with cache - very fast, very expensive.

PagingSegmentation

Very large page tables

two-level page tables

Split the page number part in two:

outer and inner page number/tables.

Each page table will now be 1K(easier to handle)

Other solutions:

64-bit architectures require more complexity: multi-level

page tables or hashed page tables.

Inverted page tables

(See section 8.5 page 297)

PagingSegmentation

Protection

Simply add a protection bits to the page table entry.

Typically: Valid/Invalid and Read/Write/Execute

Lookup in parallel: Neglectable overhead

Note that we created a problem due to internal fragmentation

PagingSegmentation

Shared pages

Example

40 users, each of whom executes a text editor

150 KB of code

50 KB of data

?We need 8 000 MB

If one copy of the text editor: Need 2 150 KB

If code is

reentrant, it can be shared.

Non self-modifying code

code state (variables, temp results) should be local to each process ?shared code pages should not be writable.

PagingSegmentation

Shared pages

Example

Compiler, Window System, run-time libraries, database systems,...

Used for shared data (Cf Process Communication)

PagingSegmentation

Segmentation

User preference

View memory as a collection of variable-sized segments, rather than a linear array of bytes Separate segments for different types of memory content: main program program libraries constants stack objects symbol table and each segment can have its own protection, grow independently, etc...

PagingSegmentation

Segmentation

User preference

Elements are identified within a segment by theiroffsetfrom the beginning of the segment

Example

the 1ststatement of the program the 7thentry of the stack the 5thinstruction of function foo()

PagingSegmentation

Segmentation

Segmentation

Memory-management scheme that supports this user view of memory Logical address space is a collection of segments. name length

Logical address

Pair:

Note: paging needs one address, implicitly split by hardware

PagingSegmentation

Address translation

User can now refer to objects in the program by a

two-dimenseional address But the actual physical memory is still a one-dimensional sequence of bytes

Must find a mapping from logical to physical

Address translation is done similar to the old memory partitions, but with baseandlimitper segment, stored in a segment table.

PagingSegmentation

Characteristics

Segmentation

"paging with variable page size"

Advantages:

memory protectionadded to segment tablelike paging sharingof memorysimilar to paging (but per area rather than per page)

Drawbacks:

allocation algorithms as for memory partitions external fragmentation, back to compaction problem...

Solution: combine segmentation and paging!

Read section 8.7 on Linux & Intel Pentium systems

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