* Guenter Roeck <linux@xxxxxxxxxxxx> [220428 16:19]: > On Tue, Apr 26, 2022 at 03:06:35PM +0000, Liam Howlett wrote: > > From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> > > > > Avoid allocating a new VMA when it a vma modification can occur. When a > > brk() can expand or contract a VMA, then the single store operation will > > only modify one index of the maple tree instead of causing a node to split > > or coalesce. This avoids unnecessary allocations/frees of maple tree > > nodes and VMAs. > > > > Move some limit & flag verifications out of the do_brk_flags() function to > > use only relevant checks in the code path of bkr() and vm_brk_flags(). > > > > Set the vma to check if it can expand in vm_brk_flags() if extra criteria > > are met. > > > > Drop userfaultfd from do_brk_flags() path and only use it in > > vm_brk_flags() path since that is the only place a munmap will happen. > > > > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > > A build failure seen when building ppc64:corenet64_smp_defconfig also > biscects to this patch. > > mm/mmap.c: In function 'do_brk_flags': > mm/mmap.c:2908:17: error: implicit declaration of function > 'khugepaged_enter_vma_merge'; did you mean 'khugepaged_enter_vma'? > > It appears that this is later fixed, but it hurts bisectability > (and prevents me from finding the actual build failure in linux-next > when trying to build corenet64_smp_defconfig). Yeah, that khugepaged_enter_vma_merge was renamed in another patch set. Andrew made the correction but kept the patch as it was. I think the suggested change is right.. if you read the commit that introduced khugepaged_enter_vma(), it seems right at least. > > While looking into the patch, I noticed the following. > > [ ... ] > > > @@ -2773,30 +2888,52 @@ static int do_brk_flags(unsigned long addr, unsigned long len, > > if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT)) > > return -ENOMEM; > > > > out: > > perf_event_mmap(vma); > > mm->total_vm += len >> PAGE_SHIFT; > > @@ -2807,18 +2944,21 @@ static int do_brk_flags(unsigned long addr, unsigned long len, > > validate_mm_mt(mm); > > return 0; > > > > -no_vma_link: > > vm_area_free(vma); > > That really looks wrong. vm_area_free(vma) can not be reached > after this patch has been applied. This came up elsewhere too, Thanks. This shouldn't cause an issue unless you OOM though. > > Guenter > > > +vma_alloc_fail: > > + vm_unacct_memory(len >> PAGE_SHIFT); > > return -ENOMEM; > > } > >
