Confusing Terms

From: gopan (gop_kumar_at_hotmail.com)
Date: 12/23/04 

Date: 22 Dec 2004 23:00:31 -0800

>1)kmalloc and Vmalloc
>2)Vmalloc and ioremap

  kmalloc is normally used when you want contiguous memory of small
size (even thou you can ask for memory sizes up to 131072 bytes). The
allocation sizes can be 32, 64, ... 131072, and if the allocation is
successful you can be sure that the allocated memory is contiguous
physically.

vmalloc is used if you want large amount of memory contiguous
virtually but not physically.

ioremap is typically used to access memory mapped devices, ie we know
the physical address where they are mapped and want to create a
mapping for them in the page tables and get a virtual address so as to
access them.

Relevant Pages

  • Re: How to use vmalloc form kernel module
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  • [patch 3/4] mm: document missing fields for /proc/meminfo
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  • Re: [PATCH 4/4] fdtable: Implement new pagesize-based fdtable allocation scheme.
    ... regardless of the size results in massive memory usage deltas. ... need the amortized power-of-two table area increase? ... I think that for such applications, the 'waste' of ram for fd table is ... vmalloc also tried to use power-of-two allocation sizes. ...
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  • Re: hash table sizes
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  • Re: [rfc][patch] dynamic resizing dentry hash using RCU
    ... So I introduce a new method for resizing hash tables with RCU, ... It should also be able to shrink under memory pressure, ... A pity it uses vmalloc memory for the moment. ... time is to add the possibility for vmallocto use hugepages ...
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