On Mon, Jul 05, 2021 at 09:09:22AM +0530, Anshuman Khandual wrote: > > > On 7/5/21 8:58 AM, Matthew Wilcox wrote: > > On Mon, Jul 05, 2021 at 08:57:54AM +0530, Anshuman Khandual wrote: > >> > >> On 7/1/21 6:27 PM, Matthew Wilcox wrote: > >>> On Thu, Jul 01, 2021 at 10:51:27AM +0530, Anshuman Khandual wrote: > >>>> > >>>> > >>>> On 5/20/21 4:47 PM, Matthew Wilcox wrote: > >>>>> On Wed, May 19, 2021 at 01:03:06PM +0530, Anshuman Khandual wrote: > >>>>>> Split ptlocks need not be defined and allocated unless they are being used. > >>>>>> ALLOC_SPLIT_PTLOCKS is inherently dependent on USE_SPLIT_PTE_PTLOCKS. This > >>>>>> just makes it explicit and clear. While here drop the spinlock_t element > >>>>>> from the struct page when USE_SPLIT_PTE_PTLOCKS is not enabled. > >>>>> > >>>>> I didn't spot this email yesterday. I'm not a fan. Isn't struct page > >>>>> already complicated enough without adding another ifdef to it? Surely > >>>>> there's a better way than this. > >>>> > >>>> This discussion thread just got dropped off the radar, sorry about it. > >>>> None of the spinlock_t elements are required unless split ptlocks are > >>>> in use. I understand your concern regarding yet another #ifdef in the > >>>> struct page definition. But this change is simple and minimal. Do you > >>>> have any other particular alternative in mind which I could explore ? > >>> > >>> Do nothing? I don't understand what problem you're trying to solve. > >> > >> Currently there is an element (spinlock_t ptl) in the struct page for page > >> table lock. Although a struct page based spinlock is not even required in > >> case USE_SPLIT_PTE_PTLOCKS evaluates to be false. Is not that something to > >> be fixed here i.e drop the splinlock_t element if not required ? > > > > No? It doesn't actually cause any problems, does it? > > No but should an unnecessary element in a struct is dropped only if there > is a reported problem ? In this case, yes. It's not just a struct member; it's a member of a union in the struct. You don't save any memory by getting rid of it. There's no benefit to getting rid of it.
