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

[Kyeongdon Kim <kyeongdon.kim@lge.com>]

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.

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