Re: Re: [PATCH v3] zram: try vmalloc() after kmalloc()

[Minchan Kim <minchan@kernel.org>]

On Tue, Nov 24, 2015 at 05:09:06PM +0900, Kyeongdon Kim wrote:
> On 2015-11-24 오전 8:28, Minchan Kim wrote:
> > 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?
> > 
> Sorry for the delay in replying,
> I just checked your comments and patch set.
> 
> [PATCH 1/3] zram/zcomp: use GFP_NOIO to allocate stream
> [PATCH 2/3] zram: try vmalloc() after kmalloc()
> [RFC 3/3] zram: pass gfp from zcomp frontend to backend
> 
> First of all, thanks for your summary and organized code set, and
> If Sergey agrees with that, I have no question about the patch 2/3.

Thanks. I will send revised version tomorrow.

> 
> >>
> > 
> > -- 
> > Kind regards,
> > Minchan Kim
> 

-- 
Kind regards,
Minchan Kim