On Fri 06-01-17 13:09:36, Vlastimil Babka wrote: > On 01/04/2017 07:12 PM, Michal Hocko wrote: > > While checking opencoded users I've encountered that vhost code would > > really like to use kvmalloc with __GFP_REPEAT [1] so the following patch > > adds support for __GFP_REPEAT and converts both vhost users. > > > > So currently I am sitting on 3 patches. I will wait for more feedback - > > especially about potential split ups or cleanups few more days and then > > repost the whole series. > > > > [1] http://lkml.kernel.org/r/20170104150800.GO25453@xxxxxxxxxxxxxx > > --- > > From 0b92e4d2e040524b878d4e7b9ee88fbad5284b33 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <mhocko@xxxxxxxx> > > Date: Wed, 4 Jan 2017 18:01:39 +0100 > > Subject: [PATCH] mm: support __GFP_REPEAT in kvmalloc_node > > > > vhost code uses __GFP_REPEAT when allocating vhost_virtqueue resp. > > vhost_vsock because it would really like to prefer kmalloc to the > > vmalloc fallback - see 23cc5a991c7a ("vhost-net: extend device > > allocation to vmalloc") for more context. Michael Tsirkin has also > > noted: > > " > > __GFP_REPEAT overhead is during allocation time. Using vmalloc means all > > accesses are slowed down. Allocation is not on data path, accesses are. > > " > > > > Let's teach kvmalloc_node to handle __GFP_REPEAT properly. There are two > > things to be careful about. First we should prevent from the OOM killer > > and so have to involve __GFP_NORETRY by default and secondly override > > __GFP_REPEAT for !costly order requests as the __GFP_REPEAT is ignored > > for !costly orders. > > > > This patch shouldn't introduce any functional change. > > Which is because the converted usages are always used for costly order, > right. I have overlooked this remark previously. You are right. And I've updated the documentation and also the inline comment to be more explicit about this. We do not have a good way to support __GFP_REPEAT for !costly orders currently unfortunatelly. Maybe I should revive my __GFP_RETRY_MAYFAIL patch, this would be another user (outside of xfs which already wants something like that for KM_MAYFAIL. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
