On Wed, Oct 29, 2025 at 9:51 AM Lorenzo Stoakes <[email protected]> wrote: > > It's useful to be able to force a VMA to be copied on fork outside of the > parameters specified by vma_needs_copy(), which otherwise only copies page > tables if: > > * The destination VMA has VM_UFFD_WP set > * The mapping is a PFN or mixed map > * The mapping is anonymous and forked in (i.e. vma->anon_vma is non-NULL) > > Setting this flag implies that the page tables mapping the VMA are such > that simply re-faulting the VMA will not re-establish them in identical > form. > > We introduce VM_COPY_ON_FORK to clearly identify which flags require this > behaviour, which currently is only VM_MAYBE_GUARD. > > Any VMA flags which require this behaviour are inherently 'sticky', that > is, should we merge two VMAs together, this implies that the newly merged > VMA maps a range that requires page table copying on fork. > > In order to implement this we must both introduce the concept of a 'sticky' > VMA flag and adjust the VMA merge logic accordingly, and also have VMA > merge still successfully succeed should one VMA have the flag set and > another not.
"successfully succeed" sounds weird. Just "succeed"? > > Note that we update the VMA expand logic to handle new VMA merging, as this > function is the one ultimately called by all instances of merging of new > VMAs. > > This patch implements this, establishing VM_STICKY to contain all such > flags and VM_IGNORE_MERGE for those flags which should be ignored when > comparing adjacent VMA's flags for the purposes of merging. > > As part of this change we place VM_SOFTDIRTY in VM_IGNORE_MERGE as it > already had this behaviour, alongside VM_STICKY as sticky flags by > implication must not disallow merge. > > We update the VMA userland tests to account for the changes and, > furthermore, in order to assert that the functionality is workingly s/workingly/working > correctly, update the new VMA and existing VMA merging logic to consider > every permutation of the flag being set/not set in all VMAs being > considered for merge. > > As a result of this change, VMAs with guard ranges will now not have their > merge behaviour impacted by doing so and can be freely merged with other > VMAs without VM_MAYBE_GUARD set. > > Signed-off-by: Lorenzo Stoakes <[email protected]> > --- > include/linux/mm.h | 32 ++++++++++++ > mm/memory.c | 3 +- > mm/vma.c | 22 ++++---- > tools/testing/vma/vma.c | 89 ++++++++++++++++++++++++++++---- > tools/testing/vma/vma_internal.h | 32 ++++++++++++ > 5 files changed, 156 insertions(+), 22 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f963afa1b9de..a8811ba57150 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -522,6 +522,38 @@ extern unsigned int kobjsize(const void *objp); > #endif > #define VM_FLAGS_CLEAR (ARCH_VM_PKEY_FLAGS | VM_ARCH_CLEAR) > > +/* Flags which should result in page tables being copied on fork. */ > +#define VM_COPY_ON_FORK VM_MAYBE_GUARD > + > +/* > + * Flags which should be 'sticky' on merge - that is, flags which, when one > VMA > + * possesses it but the other does not, the merged VMA should nonetheless > have > + * applied to it: > + * > + * VM_COPY_ON_FORK - These flags indicates that a VMA maps a range that > contains > + * metadata which should be unconditionally propagated upon > + * fork. When merging two VMAs, we encapsulate this range > in > + * the merged VMA, so the flag should be 'sticky' as a > result. It's probably worth noting that after a split, we do not remove "sticky" flags even if the VMA acquired them as a result of a previous merge. > + */ > +#define VM_STICKY VM_COPY_ON_FORK > + > +/* > + * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one > + * of these flags and the other not does not preclude a merge. > + * > + * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags > but > + * dirty bit -- the caller should mark merged VMA as dirty. If > + * dirty bit won't be excluded from comparison, we increase > + * pressure on the memory system forcing the kernel to > generate > + * new VMAs when old one could be extended instead. > + * > + * VM_STICKY - If one VMA has flags which most be 'sticky', that is ones s/most/must ? > + * which should propagate to all VMAs, but the other does not, > + * the merge should still proceed with the merge logic > applying > + * sticky flags to the final VMA. > + */ > +#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) > + > /* > * mapping from the currently active vm_flags protection bits (the > * low four bits) to a page protection mask.. > diff --git a/mm/memory.c b/mm/memory.c > index a2c79ee43d68..9528133e5147 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1478,8 +1478,7 @@ vma_needs_copy(struct vm_area_struct *dst_vma, struct > vm_area_struct *src_vma) > if (src_vma->anon_vma) > return true; > > - /* Guard regions have momdified page tables that require copying. */ > - if (src_vma->vm_flags & VM_MAYBE_GUARD) > + if (src_vma->vm_flags & VM_COPY_ON_FORK) > return true; > > /* > diff --git a/mm/vma.c b/mm/vma.c > index 919d1fc63a52..50a6909c4be3 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -89,15 +89,7 @@ static inline bool is_mergeable_vma(struct > vma_merge_struct *vmg, bool merge_nex > > if (!mpol_equal(vmg->policy, vma_policy(vma))) > return false; > - /* > - * VM_SOFTDIRTY should not prevent from VMA merging, if we > - * match the flags but dirty bit -- the caller should mark > - * merged VMA as dirty. If dirty bit won't be excluded from > - * comparison, we increase pressure on the memory system forcing > - * the kernel to generate new VMAs when old one could be > - * extended instead. > - */ > - if ((vma->vm_flags ^ vmg->vm_flags) & ~VM_SOFTDIRTY) > + if ((vma->vm_flags ^ vmg->vm_flags) & ~VM_IGNORE_MERGE) > return false; > if (vma->vm_file != vmg->file) > return false; > @@ -809,6 +801,7 @@ static bool can_merge_remove_vma(struct vm_area_struct > *vma) > static __must_check struct vm_area_struct *vma_merge_existing_range( > struct vma_merge_struct *vmg) > { > + vm_flags_t sticky_flags = vmg->vm_flags & VM_STICKY; > struct vm_area_struct *middle = vmg->middle; > struct vm_area_struct *prev = vmg->prev; > struct vm_area_struct *next; > @@ -901,11 +894,13 @@ static __must_check struct vm_area_struct > *vma_merge_existing_range( > if (merge_right) { > vma_start_write(next); > vmg->target = next; > + sticky_flags |= (next->vm_flags & VM_STICKY); > } > > if (merge_left) { > vma_start_write(prev); > vmg->target = prev; > + sticky_flags |= (prev->vm_flags & VM_STICKY); > } > > if (merge_both) { > @@ -975,6 +970,7 @@ static __must_check struct vm_area_struct > *vma_merge_existing_range( > if (err || commit_merge(vmg)) > goto abort; > > + vm_flags_set(vmg->target, sticky_flags); > khugepaged_enter_vma(vmg->target, vmg->vm_flags); > vmg->state = VMA_MERGE_SUCCESS; > return vmg->target; > @@ -1125,6 +1121,10 @@ int vma_expand(struct vma_merge_struct *vmg) > bool remove_next = false; > struct vm_area_struct *target = vmg->target; > struct vm_area_struct *next = vmg->next; > + vm_flags_t sticky_flags; > + > + sticky_flags = vmg->vm_flags & VM_STICKY; > + sticky_flags |= target->vm_flags & VM_STICKY; > > VM_WARN_ON_VMG(!target, vmg); > > @@ -1134,6 +1134,7 @@ int vma_expand(struct vma_merge_struct *vmg) > if (next && (target != next) && (vmg->end == next->vm_end)) { > int ret; > > + sticky_flags |= next->vm_flags & VM_STICKY; > remove_next = true; > /* This should already have been checked by this point. */ > VM_WARN_ON_VMG(!can_merge_remove_vma(next), vmg); > @@ -1160,6 +1161,7 @@ int vma_expand(struct vma_merge_struct *vmg) > if (commit_merge(vmg)) > goto nomem; > > + vm_flags_set(target, sticky_flags); > return 0; > > nomem: > @@ -1903,7 +1905,7 @@ static int anon_vma_compatible(struct vm_area_struct > *a, struct vm_area_struct * > return a->vm_end == b->vm_start && > mpol_equal(vma_policy(a), vma_policy(b)) && > a->vm_file == b->vm_file && > - !((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | > VM_SOFTDIRTY)) && > + !((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | > VM_IGNORE_MERGE)) && > b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> > PAGE_SHIFT); > } > > diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c > index 656e1c75b711..ee9d3547c421 100644 > --- a/tools/testing/vma/vma.c > +++ b/tools/testing/vma/vma.c I prefer tests in a separate patch, but that might just be me. Feel free to ignore. > @@ -48,6 +48,8 @@ static struct anon_vma dummy_anon_vma; > #define ASSERT_EQ(_val1, _val2) ASSERT_TRUE((_val1) == (_val2)) > #define ASSERT_NE(_val1, _val2) ASSERT_TRUE((_val1) != (_val2)) > > +#define IS_SET(_val, _flags) ((_val & _flags) == _flags) > + > static struct task_struct __current; > > struct task_struct *get_current(void) > @@ -441,7 +443,7 @@ static bool test_simple_shrink(void) > return true; > } > > -static bool test_merge_new(void) > +static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool > b_is_sticky, bool c_is_sticky) > { > vm_flags_t vm_flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE; > struct mm_struct mm = {}; > @@ -469,23 +471,32 @@ static bool test_merge_new(void) > struct vm_area_struct *vma, *vma_a, *vma_b, *vma_c, *vma_d; > bool merged; > > + if (is_sticky) > + vm_flags |= VM_STICKY; > + > /* > * 0123456789abc > * AA B CC > */ > vma_a = alloc_and_link_vma(&mm, 0, 0x2000, 0, vm_flags); > ASSERT_NE(vma_a, NULL); > + if (a_is_sticky) > + vm_flags_set(vma_a, VM_STICKY); > /* We give each VMA a single avc so we can test anon_vma duplication. > */ > INIT_LIST_HEAD(&vma_a->anon_vma_chain); > list_add(&dummy_anon_vma_chain_a.same_vma, &vma_a->anon_vma_chain); > > vma_b = alloc_and_link_vma(&mm, 0x3000, 0x4000, 3, vm_flags); > ASSERT_NE(vma_b, NULL); > + if (b_is_sticky) > + vm_flags_set(vma_b, VM_STICKY); > INIT_LIST_HEAD(&vma_b->anon_vma_chain); > list_add(&dummy_anon_vma_chain_b.same_vma, &vma_b->anon_vma_chain); > > vma_c = alloc_and_link_vma(&mm, 0xb000, 0xc000, 0xb, vm_flags); > ASSERT_NE(vma_c, NULL); > + if (c_is_sticky) > + vm_flags_set(vma_c, VM_STICKY); > INIT_LIST_HEAD(&vma_c->anon_vma_chain); > list_add(&dummy_anon_vma_chain_c.same_vma, &vma_c->anon_vma_chain); > > @@ -520,6 +531,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 3); > + if (is_sticky || a_is_sticky || b_is_sticky) > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Merge to PREVIOUS VMA. > @@ -537,6 +550,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 3); > + if (is_sticky || a_is_sticky) > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Merge to NEXT VMA. > @@ -556,6 +571,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 3); > + if (is_sticky) /* D uses is_sticky. */ > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Merge BOTH sides. > @@ -574,6 +591,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 2); > + if (is_sticky || a_is_sticky) > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Merge to NEXT VMA. > @@ -592,6 +611,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 2); > + if (is_sticky || c_is_sticky) > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Merge BOTH sides. > @@ -609,6 +630,8 @@ static bool test_merge_new(void) > ASSERT_EQ(vma->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 1); > + if (is_sticky || a_is_sticky || c_is_sticky) > + ASSERT_TRUE(IS_SET(vma->vm_flags, VM_STICKY)); > > /* > * Final state. > @@ -637,6 +660,20 @@ static bool test_merge_new(void) > return true; > } > > +static bool test_merge_new(void) > +{ > + int i, j, k, l; > + > + /* Generate every possible permutation of sticky flags. */ > + for (i = 0; i < 2; i++) > + for (j = 0; j < 2; j++) > + for (k = 0; k < 2; k++) > + for (l = 0; l < 2; l++) > + ASSERT_TRUE(__test_merge_new(i, j, k, > l)); > + > + return true; > +} > + > static bool test_vma_merge_special_flags(void) > { > vm_flags_t vm_flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE; > @@ -973,9 +1010,11 @@ static bool test_vma_merge_new_with_close(void) > return true; > } > > -static bool test_merge_existing(void) > +static bool __test_merge_existing(bool prev_is_sticky, bool > middle_is_sticky, bool next_is_sticky) > { > vm_flags_t vm_flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE; > + vm_flags_t prev_flags = vm_flags; > + vm_flags_t next_flags = vm_flags; > struct mm_struct mm = {}; > VMA_ITERATOR(vmi, &mm, 0); > struct vm_area_struct *vma, *vma_prev, *vma_next; > @@ -988,6 +1027,13 @@ static bool test_merge_existing(void) > }; > struct anon_vma_chain avc = {}; > > + if (prev_is_sticky) > + prev_flags |= VM_STICKY; > + if (middle_is_sticky) > + vm_flags |= VM_STICKY; > + if (next_is_sticky) > + next_flags |= VM_STICKY; > + > /* > * Merge right case - partial span. > * > @@ -1000,7 +1046,7 @@ static bool test_merge_existing(void) > */ > vma = alloc_and_link_vma(&mm, 0x2000, 0x6000, 2, vm_flags); > vma->vm_ops = &vm_ops; /* This should have no impact. */ > - vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, vm_flags); > + vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, next_flags); > vma_next->vm_ops = &vm_ops; /* This should have no impact. */ > vmg_set_range_anon_vma(&vmg, 0x3000, 0x6000, 3, vm_flags, > &dummy_anon_vma); > vmg.middle = vma; > @@ -1018,6 +1064,8 @@ static bool test_merge_existing(void) > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_TRUE(vma_write_started(vma_next)); > ASSERT_EQ(mm.map_count, 2); > + if (middle_is_sticky || next_is_sticky) > + ASSERT_TRUE(IS_SET(vma_next->vm_flags, VM_STICKY)); > > /* Clear down and reset. */ > ASSERT_EQ(cleanup_mm(&mm, &vmi), 2); > @@ -1033,7 +1081,7 @@ static bool test_merge_existing(void) > * NNNNNNN > */ > vma = alloc_and_link_vma(&mm, 0x2000, 0x6000, 2, vm_flags); > - vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, vm_flags); > + vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, next_flags); > vma_next->vm_ops = &vm_ops; /* This should have no impact. */ > vmg_set_range_anon_vma(&vmg, 0x2000, 0x6000, 2, vm_flags, > &dummy_anon_vma); > vmg.middle = vma; > @@ -1046,6 +1094,8 @@ static bool test_merge_existing(void) > ASSERT_EQ(vma_next->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma_next)); > ASSERT_EQ(mm.map_count, 1); > + if (middle_is_sticky || next_is_sticky) > + ASSERT_TRUE(IS_SET(vma_next->vm_flags, VM_STICKY)); > > /* Clear down and reset. We should have deleted vma. */ > ASSERT_EQ(cleanup_mm(&mm, &vmi), 1); > @@ -1060,7 +1110,7 @@ static bool test_merge_existing(void) > * 0123456789 > * PPPPPPV > */ > - vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, vm_flags); > + vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, prev_flags); > vma_prev->vm_ops = &vm_ops; /* This should have no impact. */ > vma = alloc_and_link_vma(&mm, 0x3000, 0x7000, 3, vm_flags); > vma->vm_ops = &vm_ops; /* This should have no impact. */ > @@ -1080,6 +1130,8 @@ static bool test_merge_existing(void) > ASSERT_TRUE(vma_write_started(vma_prev)); > ASSERT_TRUE(vma_write_started(vma)); > ASSERT_EQ(mm.map_count, 2); > + if (prev_is_sticky || middle_is_sticky) > + ASSERT_TRUE(IS_SET(vma_prev->vm_flags, VM_STICKY)); > > /* Clear down and reset. */ > ASSERT_EQ(cleanup_mm(&mm, &vmi), 2); > @@ -1094,7 +1146,7 @@ static bool test_merge_existing(void) > * 0123456789 > * PPPPPPP > */ > - vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, vm_flags); > + vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, prev_flags); > vma_prev->vm_ops = &vm_ops; /* This should have no impact. */ > vma = alloc_and_link_vma(&mm, 0x3000, 0x7000, 3, vm_flags); > vmg_set_range_anon_vma(&vmg, 0x3000, 0x7000, 3, vm_flags, > &dummy_anon_vma); > @@ -1109,6 +1161,8 @@ static bool test_merge_existing(void) > ASSERT_EQ(vma_prev->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma_prev)); > ASSERT_EQ(mm.map_count, 1); > + if (prev_is_sticky || middle_is_sticky) > + ASSERT_TRUE(IS_SET(vma_prev->vm_flags, VM_STICKY)); > > /* Clear down and reset. We should have deleted vma. */ > ASSERT_EQ(cleanup_mm(&mm, &vmi), 1); > @@ -1123,10 +1177,10 @@ static bool test_merge_existing(void) > * 0123456789 > * PPPPPPPPPP > */ > - vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, vm_flags); > + vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, prev_flags); > vma_prev->vm_ops = &vm_ops; /* This should have no impact. */ > vma = alloc_and_link_vma(&mm, 0x3000, 0x7000, 3, vm_flags); > - vma_next = alloc_and_link_vma(&mm, 0x7000, 0x9000, 7, vm_flags); > + vma_next = alloc_and_link_vma(&mm, 0x7000, 0x9000, 7, next_flags); > vmg_set_range_anon_vma(&vmg, 0x3000, 0x7000, 3, vm_flags, > &dummy_anon_vma); > vmg.prev = vma_prev; > vmg.middle = vma; > @@ -1139,6 +1193,8 @@ static bool test_merge_existing(void) > ASSERT_EQ(vma_prev->anon_vma, &dummy_anon_vma); > ASSERT_TRUE(vma_write_started(vma_prev)); > ASSERT_EQ(mm.map_count, 1); > + if (prev_is_sticky || middle_is_sticky || next_is_sticky) > + ASSERT_TRUE(IS_SET(vma_prev->vm_flags, VM_STICKY)); > > /* Clear down and reset. We should have deleted prev and next. */ > ASSERT_EQ(cleanup_mm(&mm, &vmi), 1); > @@ -1158,9 +1214,9 @@ static bool test_merge_existing(void) > * PPPVVVVVNNN > */ > > - vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, vm_flags); > + vma_prev = alloc_and_link_vma(&mm, 0, 0x3000, 0, prev_flags); > vma = alloc_and_link_vma(&mm, 0x3000, 0x8000, 3, vm_flags); > - vma_next = alloc_and_link_vma(&mm, 0x8000, 0xa000, 8, vm_flags); > + vma_next = alloc_and_link_vma(&mm, 0x8000, 0xa000, 8, next_flags); > > vmg_set_range(&vmg, 0x4000, 0x5000, 4, vm_flags); > vmg.prev = vma; > @@ -1203,6 +1259,19 @@ static bool test_merge_existing(void) > return true; > } > > +static bool test_merge_existing(void) > +{ > + int i, j, k; > + > + /* Generate every possible permutation of sticky flags. */ > + for (i = 0; i < 2; i++) > + for (j = 0; j < 2; j++) > + for (k = 0; k < 2; k++) > + ASSERT_TRUE(__test_merge_existing(i, j, k)); > + > + return true; > +} > + > static bool test_anon_vma_non_mergeable(void) > { > vm_flags_t vm_flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE; > diff --git a/tools/testing/vma/vma_internal.h > b/tools/testing/vma/vma_internal.h > index e40c93edc5a7..3d9cb3a9411a 100644 > --- a/tools/testing/vma/vma_internal.h > +++ b/tools/testing/vma/vma_internal.h > @@ -117,6 +117,38 @@ extern unsigned long dac_mmap_min_addr; > #define VM_SEALED VM_NONE > #endif > > +/* Flags which should result in page tables being copied on fork. */ > +#define VM_COPY_ON_FORK VM_MAYBE_GUARD > + > +/* > + * Flags which should be 'sticky' on merge - that is, flags which, when one > VMA > + * possesses it but the other does not, the merged VMA should nonetheless > have > + * applied to it: > + * > + * VM_COPY_ON_FORK - These flags indicates that a VMA maps a range that > contains > + * metadata which should be unconditionally propagated upon > + * fork. When merging two VMAs, we encapsulate this range > in > + * the merged VMA, so the flag should be 'sticky' as a > result. > + */ > +#define VM_STICKY VM_COPY_ON_FORK > + > +/* > + * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one > + * of these flags and the other not does not preclude a merge. > + * > + * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags > but > + * dirty bit -- the caller should mark merged VMA as dirty. If > + * dirty bit won't be excluded from comparison, we increase > + * pressure on the memory system forcing the kernel to > generate > + * new VMAs when old one could be extended instead. > + * > + * VM_STICKY - If one VMA has flags which must be 'sticky', that is ones > + * which should propagate to all VMAs, but the other does not, > + * the merge should still proceed with the merge logic > applying > + * sticky flags to the final VMA. > + */ > +#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) > + > #define FIRST_USER_ADDRESS 0UL > #define USER_PGTABLES_CEILING 0UL > > -- > 2.51.0 >
