Messages in this thread |  | | Date | Sat, 15 Nov 2008 21:47:35 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 1/7] mm: introduce simple_malloc()/simple_free() |
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On Sun, 16 Nov 2008 13:35:03 +0800 Lai Jiangshan <laijs@cn.fujitsu.com> wrote:
> Andrew Morton wrote: > > On Sat, 15 Nov 2008 20:52:29 -0800 Arjan van de Ven <arjan@infradead.org> wrote: > > > >> On Sun, 16 Nov 2008 12:33:15 +0800 > >> Lai Jiangshan <laijs@cn.fujitsu.com> wrote: > >> > >>> some subsystem needs vmalloc() when required memory is large. > >>> but current kernel has not APIs for this requirement. > >>> this patch introduces simple_malloc() and simple_free(). > >> Hi > >> > >> I kinda really don't like this approach. vmalloc() (and especially, > >> vfree()) is a really expensive operation, and vmalloc()'d memory is > >> also slower (due to tlb pressure). > > > > And it can fragment, which effectively means a dead box. > > > >> Realistically, people should try hard > >> to use small datastructure instead.... > > > > Yup, it makes it easier for people to do something which we strongly > > discourage. The risk got worse with all these 64-bit machines with > > vast amounts of virtual address space. It makes it easier for people > > to develop and "test" code which isn't reliable on smaller machines. > > > > > > vmalloc() is not good for performance and increasing fragment. > but vmalloc() is need for some subsystems' alternative malloc, > like cgroup's tasks file and other subsystems(about 20 subsystems). > > these subsystems use kmalloc() in the most condition, but may need > vmalloc() in some rare condition. so they use alternative malloc. > > So, since these subsystems' maintainer have good reasons for using vmalloc(), > they can use simple_malloc() too. simple_malloc() is not for common using. > (I should document when we use simple_malloc() in the code) > > simple_free() is useful. there are several subsystems which use a flags > for selecting kfree() or vfree(), and some subsystems recount the size hardy > before kfree() or vfree(). >
Sure. Apart from the names of the functions, it's a good cleanup of existing code.
It's just that we must *really* discourage the use of vmalloc :(
Maybe we should call it i_am_a_hopeless_loser_alloc(). Sending the per-subsystem patches to the maintainers would be fun.
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