Hi Thomas, On 2/19/2018 3:16 PM, Thomas Gleixner wrote: > On Mon, 19 Feb 2018, Reinette Chatre wrote: >> On 2/19/2018 12:57 PM, Thomas Gleixner wrote: >>> On Tue, 13 Feb 2018, Reinette Chatre wrote: >>> >>>> System administrator creates/removes pseudo-locked regions by >>>> creating/removing directories in the pseudo-lock subdirectory of the >>>> resctrl filesystem. Here we add directory creation and removal support. >>>> >>>> A "pseudo-lock region" is introduced, which represents an >>>> instance of a pseudo-locked cache region. During mkdir a new region is >>>> created but since we do not know which cache it belongs to at that time >>>> we maintain a global pointer to it from where it will be moved to the cache >>>> (rdt_domain) it belongs to after initialization. This implies that >>>> we only support one uninitialized pseudo-locked region at a time. >>> >>> Whats the reason for this restriction? If there are uninitialized >>> directories, so what? >> >> I was thinking about a problematic scenario where an application >> attempts to create infinite directories. All of these uninitialized >> directories need to be kept track of before they are initialized as >> pseudo-locked regions. It seemed simpler to require that one >> pseudo-locked region is set up at a time. > > If the application is allowed to create directories then it can also create > a dozen unused resource control groups. This is not a Joe User operation so > there is no problem.
Thank you for the guidance. I will remove this restriction. >>>> +/* >>>> + * rdt_pseudo_lock_rmdir - Remove pseudo-lock region >>>> + * >>>> + * LOCKING: >>>> + * Since the pseudo-locked region can be associated with a RDT domain at >>>> + * removal we take both rdtgroup_mutex and rdt_pseudo_lock_mutex to >>>> protect >>>> + * the rdt_domain access as well as the pseudo_lock_region access. >>> >>> Is there a real reason / benefit for having this second mutex? >> >> Some interactions with the pseudo-locked region are currently done >> without the need for the rdtgroup_mutex. For example, interaction with >> the character device associated with the pseudo-locked region (the >> mmap() call) as well as the debugfs operations. > > Well, yes. But none of those operations are hot path so having the double > locking in lots of the other function is just extra complexity for no real > value. I will revise. Thank you very much. Reinette
