On Wed 11-01-17 08:35:27, Vlastimil Babka wrote: > [+CC linux-api] > > On 01/11/2017 01:15 AM, David Rientjes wrote: > > There is no thp defrag option that currently allows MADV_HUGEPAGE regions > > to do direct compaction and reclaim while all other thp allocations simply > > trigger kswapd and kcompactd in the background and fail immediately. > > > > The "defer" setting simply triggers background reclaim and compaction for > > all regions, regardless of MADV_HUGEPAGE, which makes it unusable for our > > userspace where MADV_HUGEPAGE is being used to indicate the application is > > willing to wait for work for thp memory to be available. > > > > The "madvise" setting will do direct compaction and reclaim for these > > MADV_HUGEPAGE regions, but does not trigger kswapd and kcompactd in the > > background for anybody else. > > > > For reasonable usage, there needs to be a mesh between the two options. > > This patch introduces a fifth mode, "defer+madvise", that will do direct > > reclaim and compaction for MADV_HUGEPAGE regions and trigger background > > reclaim and compaction for everybody else so that hugepages may be > > available in the near future. > > > > A proposal to allow direct reclaim and compaction for MADV_HUGEPAGE > > regions as part of the "defer" mode, making it a very powerful setting and > > avoids breaking userspace, was offered: > > http://marc.info/?t=148236612700003. This additional mode is a > > compromise. > > > > A second proposal to allow both "defer" and "madvise" to be selected at > > the same time was also offered: http://marc.info/?t=148357345300001. > > This is possible, but there was a concern that it might break existing > > userspaces the parse the output of the defrag mode, so the fifth option > > was introduced instead. > > > > This patch also cleans up the helper function for storing to "enabled" > > and "defrag" since the former supports three modes while the latter > > supports five and triple_flag_store() was getting unnecessarily messy. > > > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> > > alloc_hugepage_direct_gfpmask() would have been IMHO simpler if a new > internal flag wasn't added, and combination of two existing for defer > and madvise used, I agree with Vlastimil here. The patch can do without touching anything outside of the sysfs handling. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
