Messages in this thread | | | Date | Tue, 24 Nov 2015 09:30:27 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH] zram/zcomp: use GFP_NOIO to allocate streams |
| |
On (11/23/15 15:18), Andrew Morton wrote: [..] > > --- a/drivers/block/zram/zcomp_lz4.c > > +++ b/drivers/block/zram/zcomp_lz4.c > > @@ -20,10 +20,13 @@ static void *zcomp_lz4_create(void) > > void *ret; > > > > ret = kzalloc(LZ4_MEM_COMPRESS, > > - __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC); > > - if (!ret) > > - ret = vzalloc(LZ4_MEM_COMPRESS); > > - return ret; > > + __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC); > > But here we've still lost __GFP_RECLAIM, unnecessarily. And it's quite > unclear why __GFP_NORETRY and __GFP_NOMEMALLOC are being used.
__GFP_NORETRY
we are guaranteed to have at least one compression stream, so sooner or later every IO operation will be served. any IO that has failed in zcomp_lz4_create() or zcomp_lzo_create() will simply wait for already available compression stream to become idle. so this allocation is not so dramatically important - we just increase the level of parallelism (N idle streams let N IO operations to execute concurrently). apart from that we are in a low memory condition (or whatever was the reason the kernel failed to allocate LZ4_MEM_COMPRESS or LZO1X_MEM_COMPRESS) and we can avoid pressuring the kernel furher.
for the same reason __GFP_NOMEMALLOC is used -- we don't want to waste an emergency memory for compression streams.
I agree on __GFP_RECLAIM. Thanks.
> IOW, why not simply use (GFP_NOIO|__GFP_NOWARN)?
GFP_NOIO | __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC ?
-ss
| |