Messages in this thread | | | Date | Mon, 23 Nov 2015 14:52:26 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v3] zram: try vmalloc() after kmalloc() |
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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 GFP_KERNEL, what's the point in clearing those flags for the kmalloc() case?
If this change (or something like it) remains in place, it should have a comment which fully explains the reasons, please.
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