On 2016/12/15 23:07, Michal Hocko wrote: > GFP_NOFS context is used for the following 5 reasons currently > - to prevent from deadlocks when the lock held by the allocation > context would be needed during the memory reclaim > - to prevent from stack overflows during the reclaim because > the allocation is performed from a deep context already > - to prevent lockups when the allocation context depends on > other reclaimers to make a forward progress indirectly > - just in case because this would be safe from the fs POV > - silence lockdep false positives > > Unfortunately overuse of this allocation context brings some problems > to the MM. Memory reclaim is much weaker (especially during heavy FS > metadata workloads), OOM killer cannot be invoked because the MM layer > doesn't have enough information about how much memory is freeable by the > FS layer. This series is intended for simply applying "& ~__GFP_FS" mask to allocations which are using GFP_KERNEL by error for the current thread, isn't it? > > In many cases it is far from clear why the weaker context is even used > and so it might be used unnecessarily. We would like to get rid of > those as much as possible. One way to do that is to use the flag in > scopes rather than isolated cases. Such a scope is declared when really > necessary, tracked per task and all the allocation requests from within > the context will simply inherit the GFP_NOFS semantic. > > Not only this is easier to understand and maintain because there are > much less problematic contexts than specific allocation requests, this > also helps code paths where FS layer interacts with other layers (e.g. > crypto, security modules, MM etc...) and there is no easy way to convey > the allocation context between the layers. I haven't heard an answer to "a terrible thing" in http://lkml.kernel.org/r/20160427200530.GB22544@xxxxxxxxxxxxxx . What is your plan for checking whether we need to propagate "& ~__GFP_FS" mask to other threads which current thread waits synchronously (e.g. wait_for_completion()) from "& ~__GFP_FS" context? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>