Re: [PATCH] Remove OOM killer from try_to_free_pages / all_unreclaimable braindamage

Nikita Danilov
2004-11-06T16:54:45Z

Andrea Arcangeli writes:
> On Sat, Nov 06, 2004 at 02:37:05PM +0300, Nikita Danilov wrote:
> > We need page-reservation API of some sort. There were several attempts
> > to introduce this, but none get into mainline.
>
> they're already in under the name of mempools

I am talking about slightly different thing. Think of some operation
that calls find_or_create_page(). find_or_create_page() doesn't know
about memory reserved in mempools, it uses alloc_page() directly. If one
wants to guarantee that compound operation has enough memory to
complete, memory should be reserved at the lowest level---in the page
allocator.

>
> I'm perfectly aware the fs tends to be the less correct places in terms
> of allocations, and luckily it's not an heavy memory user, so I still

Either you are kidding, or we are facing very different workloads. In
the world of file-system development, file-system is (not surprisingly)
single largest memory consumer.

> have to see a deadlock in getblk or create_buffers or similar. It's
> mostly a correctness issue (math proof it can't deadlock, right now it
> can if more tasks all get stuck in getblk at the same time during a hard
> oom condition etc..).

Add here mmap that can dirty all physical memory behind your back, and
delayed disk block allocation that forces ->writepage() to allocate
potentially huge extent when memory is already tight and hope of having
a proof becomes quite remote.

Nikita.