Messages in this thread |  | | Date | Sun, 7 Oct 2001 00:31:27 +0200 (CEST) | From | Mikulas Patocka <> | Subject | Re: %u-order allocation failed |
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> > It is perfectly OK to have a bit slower access to task_struct with > > probability 1/1000000. > > Except that you added a bug where some old driver code would crash the > machine by doing so.
?
> > Yes, but there are still other dangerous usages of kmalloc and > > __get_free_pages. (The most offending one is in select.c) > > Nothing dangeorus there. The -ac vm isnt triggering these cases.
Sorry, but it can be triggered by _ANY_ VM since buddy allocator was introduced. You have no guarantee, that you find two or more consecutive free pages. And if you don't, poll() fails.
> > not abort his operation when it happens. Instead - they are trying to make > > high-order allocations fail less often :-/ How should random > > Joe-driver-developer know, that kmalloc(4096) is safe and kmalloc(4097) is > > not? > > 4096 is not safe - there is no safe size for a kmalloc, you can always run > out of memory - deal with it.
This is not about running out of memory. It is about free space fragmentation. Think this:
You have no swap. Program allocates one file cache page, one anon page, one cache page, one anon page and so on. The memory will look like:
cache page anon page cache page anon page cache page anon page etc.
Now some driver wants to allocate 4097 and it CAN'T. Even when there's half memory free.
Mikulas
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