Messages in this thread | | | Date | Tue, 24 Nov 2015 08:28:57 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH v3] zram: try vmalloc() after kmalloc() |
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Hello Andrew,
On Mon, Nov 23, 2015 at 02:52:26PM -0800, Andrew Morton wrote: > On Mon, 23 Nov 2015 15:21:15 +0900 Kyeongdon Kim <kyeongdon.kim@lge.com> wrote: > > > When we're using LZ4 multi compression streams for zram swap, > > we found out page allocation failure message in system running test. > > That was not only once, but a few(2 - 5 times per test). > > Also, some failure cases were continually occurring to try allocation > > order 3. > > > > In order to make parallel compression private data, we should call > > kzalloc() with order 2/3 in runtime(lzo/lz4). But if there is no order > > 2/3 size memory to allocate in that time, page allocation fails. > > This patch makes to use vmalloc() as fallback of kmalloc(), this > > prevents page alloc failure warning. > > > > After using this, we never found warning message in running test, also > > It could reduce process startup latency about 60-120ms in each case. > > > > ... > > > > --- a/drivers/block/zram/zcomp_lz4.c > > +++ b/drivers/block/zram/zcomp_lz4.c > > @@ -10,17 +10,25 @@ > > #include <linux/kernel.h> > > #include <linux/slab.h> > > #include <linux/lz4.h> > > +#include <linux/vmalloc.h> > > +#include <linux/mm.h> > > > > #include "zcomp_lz4.h" > > > > static void *zcomp_lz4_create(void) > > { > > - return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL); > > + void *ret; > > + > > + ret = kzalloc(LZ4_MEM_COMPRESS, > > + __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC); > > + if (!ret) > > + ret = vzalloc(LZ4_MEM_COMPRESS); > > + return ret; > > } > > What's the reasoning behind the modification to the gfp flags? > > It clears __GFP_FS, __GFP_IO and even __GFP_WAIT. I suspect the latter > two (at least) can be retained. And given that vmalloc() uses
This function is used in swapout and fs write path so we couldn't use those flags.
> GFP_KERNEL, what's the point in clearing those flags for the kmalloc() > case?
When I reviewed this patch, I wanted to fix it with another patch because we should handle another places in zcomp and Sergey sent it today. But I think Sergey's patch is stable material so I hope Kyeongdon resend this patch with fixing vmalloc part.
> > If this change (or something like it) remains in place, it should have > a comment which fully explains the reasons, please.
Kyeongdon, Could you resend this patch with fixing vzalloc part and adding comment?
>
-- Kind regards, Minchan Kim
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