On Wed 27-04-16 08:58:45, Dave Chinner wrote: > On Tue, Apr 26, 2016 at 01:56:12PM +0200, Michal Hocko wrote: > > From: Michal Hocko <[email protected]> > > > > THIS PATCH IS FOR TESTING ONLY AND NOT MEANT TO HIT LINUS TREE > > > > It is desirable to reduce the direct GFP_NO{FS,IO} usage at minimum and > > prefer scope usage defined by memalloc_no{fs,io}_{save,restore} API. > > > > Let's help this process and add a debugging tool to catch when an > > explicit allocation request for GFP_NO{FS,IO} is done from the scope > > context. The printed stacktrace should help to identify the caller > > and evaluate whether it can be changed to use a wider context or whether > > it is called from another potentially dangerous context which needs > > a scope protection as well. > > You're going to get a large number of these from XFS. There are call > paths in XFs that get called both inside and outside transaction > context, and many of them are marked with GFP_NOFS to prevent issues > that have cropped up in the past. > > Often these are to silence lockdep warnings (e.g. commit b17cb36 > ("xfs: fix missing KM_NOFS tags to keep lockdep happy")) because > lockdep gets very unhappy about the same functions being called with > different reclaim contexts. e.g. directory block mapping might > occur from readdir (no transaction context) or within transactions > (create/unlink). hence paths like this are tagged with GFP_NOFS to > stop lockdep emitting false positive warnings....
I would much rather see lockdep being fixed than abusing GFP_NOFS to workaround its limitations. GFP_NOFS has a real consequences to the memory reclaim. I will go and check the commit you mentioned and try to understand why that is a problem. From what you described above I would like to get rid of exactly this kind of usage which is not really needed for the recursion protection. Thanks! -- Michal Hocko SUSE Labs ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
