On Wed, 26 Nov 2014 14:40:06 -0800 (PST) David Rientjes <[email protected]>
wrote:
> On Wed, 26 Nov 2014, Andrew Morton wrote:
>
> > You forgot something.
> >
> > ---
> > a/fs/seq_file.c~fs-seq_file-fallback-to-vmalloc-instead-of-oom-kill-processes-fix
> > +++ a/fs/seq_file.c
> > @@ -36,6 +36,10 @@ static void *seq_buf_alloc(unsigned long
> > {
> > void *buf;
> >
> > + /*
> > + * __GFP_NORETRY to avoid oom-killings with high-order allocations -
> > + * it's better to fall back to vmalloc() than to kill things.
> > + */
> > buf = kmalloc(size, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
> > if (!buf && size > PAGE_SIZE)
> > buf = vmalloc(size);
> >
>
> ...
>
> The slowpath tries to allocate, calls memory compaction if necessary,
> tries to allocate, calls direct reclaim, tries to allocate, call the oom
> killer and tries to allocate if we are going to loop, and then loop if
> allowed. There's no need to try to allocate if we don't call the oom
> killer since it won't succeed and there's no need to call the oom killer
> to free memory if we aren't going to retry.
My concern is that an open-coded __GFP_NORETRY is very obscure. Even
something like
#define __GFP_NO_OOM_KILL __GFP_NORETRY
would help make things a bit self-documenting.
> Even if __GFP_NO_OOM_KILL existed, it wouldn't be applicable to this
> patch: the change here is that seqfile will now return -ENOMEM instead of
> oom killing processes;
Not really? The change makes seq_buf_alloc() fall back to vmalloc()
rather than killing things. Doesn't it?
Unless the allocation is < PAGE_SIZE, in which case we do go ENOMEM.
That's daft - it would be better to vmalloc() a whole page in this
case. Not that the vmalloc is likely to be successful anyway..
> the slab allocation will no longer loop forever
> trying to allocate memory.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
