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 OWOsutzj 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 05, 2025 at 03:59:28PM +0000, Matthew Wilcox wrote: > On Wed, Mar 05, 2025 at 02:55:06PM +0000, Lorenzo Stoakes wrote: > > So adding additional fields is generally unviable, and VMA flags are > > equally as contended, and prevent VMA merge, further impacting overhead. > > > > We can however make use of the time-honoured kernel tradition of grabbing > > bits where we can. > > > > Since we can rely upon anon_vma allocations being at least system > > word-aligned, we have a handful of bits in the vma->anon_vma available to > > use as flags. > > I'm not a huge fan when there's a much better solution. It's an > unsigned long, but we can only use the first 32 bits because of 32-bit > compatibility? This is a noose we've made for our own neck. Sure, as discussed off-list this is something I'm going to look at, it's not either/or at all :) I have in the back of my mind _other uses_ for these flags which isn't stated here (perhaps should be), perhaps we can have other kinds of data type we reference here. But perhaps it's a bit early for that... Other than that was a morning's work to see if this _could_ work as a _immediate_ 'what can we do to address this issue?' solution. The vm_flags solution is viable, as we can modify merging behaviour for a 'sticky' VMA flag that doesn't impact merging, i.e. mask out for merge compatibility testing, but ensure propagated on split/merge (same behaviour as what the anon_vma flags achieve). > > (there are many more places to fix up; this is illustrative): > > diff --git a/include/linux/hugetlb_inline.h b/include/linux/hugetlb_inline.h > index 0660a03d37d9..c6ea81ff4afe 100644 > --- a/include/linux/hugetlb_inline.h > +++ b/include/linux/hugetlb_inline.h > @@ -8,7 +8,7 @@ > > static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma) > { > - return !!(vma->vm_flags & VM_HUGETLB); > + return test_bit(VM_HUGETLB, vma->vm_flags); > } > > #else > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 0ca9feec67b8..763210ba70b6 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -571,7 +571,8 @@ static inline void *folio_get_private(struct folio *folio) > return folio->private; > } > > -typedef unsigned long vm_flags_t; > +#define VM_FLAGS_COUNT (8 / sizeof(unsigned long)) > +typedef unsigned long vm_flags_t[VM_FLAGS_COUNT]; > > /* > * A region containing a mapping of a non-memory backed file under NOMMU Ohhhh does test_bit() automagically figure things out for sizeof(addr) including on 32-bit? Maybe I can quickly slap together something for that quicker than I thought then? I was _very concerned_ about tearing and that being a total PITA hence deferring a bit. But... if you're saying I can churn this to death and it'll 'just work' then say no more... ;) Let's put this on hold then until/when I have actual reasons to have different anon_vma types and I'll look at the 'make vm_flags 64-bit everywhere' thing instead.