Messages in this thread | | | Date | Tue, 24 Nov 2015 16:03:11 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH 2/3] zram: try vmalloc() after kmalloc() |
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On Tue, Nov 24, 2015 at 03:12:58PM +0900, Sergey Senozhatsky wrote: > [..] > > static void *zcomp_lz4_create(void) > > { > > - return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL); > > + void *ret; > > + > > + /* > > + * This function could be called in swapout/fs write path > > + * so we couldn't use GFP_FS|IO. And it assumes we already > > + * have at least one stream in zram initialization so we > > + * don't do best effort to allocate more stream in here. > > + * A default stream will work well without further multiple > > + * stream. That's why we use __GFP_NORETRY|NOWARN|NOMEMALLOC. > > + */ > > + ret = kzalloc(LZ4_MEM_COMPRESS, > > + __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC); > > + if (!ret) > > + ret = __vmalloc(LZ4_MEM_COMPRESS, > > + __GFP_NORETRY|__GFP_NOWARN| > > + __GFP_NOMEMALLOC|__GFP_ZERO, > > + PAGE_KERNEL); > > + return ret; > > } > [..] > > so this change is still questionable. is there a real value in having > a vmalloc() fallback in the middle of allocations sequence: > > zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO); > ^^^ ok, can fail here > > zstrm->zstrm->private = comp->backend->create(); > ^^^ kzalloc() and vmalloc() fallback ?? > > zstrm->buffer = (void *)__get_free_pages(GFP_NOIO | __GFP_ZERO, 1); > ^^^ can fail here again. > > can you please comment on this?
Good question.
Actually, failure of allocation came from backend->create as Kyeongdon's comment because it requires order-3 allocation which is very fragile in embedded system recenlty(Android, webOS. That's why Joonsoo are solving the trouble by fixing compaction part). Otherwise, other kmalloc/vmalloc stuff in our example would be almost no trouble in real practice(Of course, if you says it might, you're absolutely right. It could fail but I think it's *really* rare in real practice).
More concern is order-1 allocation rather than kmalloc/vmalloc. I've got lots of allocation failure reports from product team until now and frankly speaking, I don't get such order-1 fail report until now. I guess the reason is that system is almost trobule due to heavy fragmentation before the notice such failure.
So, I think if we solve order-3 allocation in backend->create, above problem will be almost solved.
> > > and I'd prefer it to be a bit different -- use likely path first and > avoid an assignment in unlikely path.
Personally, I like one return case unless other is really better for performance. I have trained it for Andrew, I belive. :) But if you don't like this by performance reason, I will add unlikely for vmalloc path. If you hate it just by personal preferenece, please I want to stick my code.
> ... and add GFP_NOIO to both kzalloc() and __vmalloc().
I can add it. The harmness is really ignorable but as I mentioned at reply of Andrew, what's the benefit with GFP_NOIO? We couldn't make forward progress with __GFP_RECLAIM in reclaim context.
> > and there is no __GFP_HIGHMEM in __vmalloc() call?
Good to have. Thanks for the hint!
Thanks.
> > something like this: > > --- > > > ret = kzalloc(LZ4_MEM_COMPRESS, GFP_NOIO | __GFP_NORETRY | > __GFP_NOWARN | __GFP_NOMEMALLOC); > if (ret) > return ret; > > return __vmalloc(LZ4_MEM_COMPRESS, > GFP_NOIO | __GFP_NOWARN | __GFP_HIGHMEM | __GFP_ZERO, > PAGE_KERNEL); > > > -ss
-- Kind regards, Minchan Kim
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