Quite a few userfaultfd functions took both mm and vma pointers as
arguments. Since the mm is trivially accessible via vma->vm_mm, there's
no reason to pass both; it just needlessly extends the already long
argument list.
Get rid of the mm pointer, where possible, to shorten the argument list.
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
fs/userfaultfd.c | 2 +-
include/linux/hugetlb.h | 5 ++-
include/linux/shmem_fs.h | 4 +--
include/linux/userfaultfd_k.h | 4 +--
mm/hugetlb.c | 9 +++--
mm/shmem.c | 7 ++--
mm/userfaultfd.c | 66 ++++++++++++++++-------------------
7 files changed, 45 insertions(+), 52 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 365bf00dd8dd..84d5d402214a 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1629,7 +1629,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
/* Reset ptes for the whole vma range if wr-protected */
if (userfaultfd_wp(vma))
- uffd_wp_range(mm, vma, start, vma_end - start, false);
+ uffd_wp_range(vma, start, vma_end - start, false);
new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 8f0467bf1cbd..8b9325f77ac3 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -158,7 +158,7 @@ unsigned long hugetlb_total_pages(void);
vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, unsigned int flags);
#ifdef CONFIG_USERFAULTFD
-int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte,
+int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
@@ -393,8 +393,7 @@ static inline void hugetlb_free_pgd_range(struct mmu_gather *tlb,
}
#ifdef CONFIG_USERFAULTFD
-static inline int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
- pte_t *dst_pte,
+static inline int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 103d1000a5a2..b82916c25e61 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -151,14 +151,14 @@ extern void shmem_uncharge(struct inode *inode, long pages);
#ifdef CONFIG_USERFAULTFD
#ifdef CONFIG_SHMEM
-extern int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+extern int shmem_mfill_atomic_pte(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
bool zeropage, bool wp_copy,
struct page **pagep);
#else /* !CONFIG_SHMEM */
-#define shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, \
+#define shmem_mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, \
src_addr, zeropage, wp_copy, pagep) ({ BUG(); 0; })
#endif /* CONFIG_SHMEM */
#endif /* CONFIG_USERFAULTFD */
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 468080125612..ba79e296fcc7 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -56,7 +56,7 @@ enum mcopy_atomic_mode {
MCOPY_ATOMIC_CONTINUE,
};
-extern int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+extern int mfill_atomic_install_pte(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr, struct page *page,
bool newly_allocated, bool wp_copy);
@@ -73,7 +73,7 @@ extern ssize_t mfill_atomic_continue(struct mm_struct *dst_mm, unsigned long dst
extern int mwriteprotect_range(struct mm_struct *dst_mm,
unsigned long start, unsigned long len,
bool enable_wp, atomic_t *mmap_changing);
-extern long uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *vma,
+extern long uffd_wp_range(struct vm_area_struct *vma,
unsigned long start, unsigned long len, bool enable_wp);
/* mm helpers */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4c9276549394..b4bda5f7f29f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6157,8 +6157,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* Used by userfaultfd UFFDIO_* ioctls. Based on userfaultfd's mfill_atomic_pte
* with modifications for hugetlb pages.
*/
-int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
- pte_t *dst_pte,
+int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
@@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
folio_in_pagecache = true;
}
- ptl = huge_pte_lock(h, dst_mm, dst_pte);
+ ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte);
ret = -EIO;
if (folio_test_hwpoison(folio))
@@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
if (wp_copy)
_dst_pte = huge_pte_mkuffd_wp(_dst_pte);
- set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+ set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
- hugetlb_count_add(pages_per_huge_page(h), dst_mm);
+ hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm);
/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
diff --git a/mm/shmem.c b/mm/shmem.c
index 448f393d8ab2..1d751b6cf1ac 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2415,8 +2415,7 @@ static struct inode *shmem_get_inode(struct mnt_idmap *idmap, struct super_block
}
#ifdef CONFIG_USERFAULTFD
-int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
+int shmem_mfill_atomic_pte(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
@@ -2506,11 +2505,11 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
goto out_release;
ret = shmem_add_to_page_cache(folio, mapping, pgoff, NULL,
- gfp & GFP_RECLAIM_MASK, dst_mm);
+ gfp & GFP_RECLAIM_MASK, dst_vma->vm_mm);
if (ret)
goto out_release;
- ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+ ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
&folio->page, true, wp_copy);
if (ret)
goto out_delete_from_cache;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 84db5b2fad3a..bd3542d5408f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -55,7 +55,7 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
* This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
* and anon, and for both shared and private VMAs.
*/
-int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+int mfill_atomic_install_pte(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr, struct page *page,
bool newly_allocated, bool wp_copy)
@@ -79,7 +79,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
if (wp_copy)
_dst_pte = pte_mkuffd_wp(_dst_pte);
- dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+ dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
if (vma_is_shmem(dst_vma)) {
/* serialize against truncate with the page table lock */
@@ -115,9 +115,9 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
* Must happen after rmap, as mm_counter() checks mapping (via
* PageAnon()), which is set by __page_set_anon_rmap().
*/
- inc_mm_counter(dst_mm, mm_counter(page));
+ inc_mm_counter(dst_vma->vm_mm, mm_counter(page));
- set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+ set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
@@ -127,8 +127,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
return ret;
}
-static int mfill_atomic_pte_copy(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
+static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
@@ -190,10 +189,10 @@ static int mfill_atomic_pte_copy(struct mm_struct *dst_mm,
__SetPageUptodate(page);
ret = -ENOMEM;
- if (mem_cgroup_charge(page_folio(page), dst_mm, GFP_KERNEL))
+ if (mem_cgroup_charge(page_folio(page), dst_vma->vm_mm, GFP_KERNEL))
goto out_release;
- ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+ ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
page, true, wp_copy);
if (ret)
goto out_release;
@@ -204,8 +203,7 @@ static int mfill_atomic_pte_copy(struct mm_struct *dst_mm,
goto out;
}
-static int mfill_atomic_pte_zeropage(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
+static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr)
{
@@ -217,7 +215,7 @@ static int mfill_atomic_pte_zeropage(struct mm_struct *dst_mm,
_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
dst_vma->vm_page_prot));
- dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+ dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
if (dst_vma->vm_file) {
/* the shmem MAP_PRIVATE case requires checking the i_size */
inode = dst_vma->vm_file->f_inode;
@@ -230,7 +228,7 @@ static int mfill_atomic_pte_zeropage(struct mm_struct *dst_mm,
ret = -EEXIST;
if (!pte_none(*dst_pte))
goto out_unlock;
- set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+ set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
ret = 0;
@@ -240,8 +238,7 @@ static int mfill_atomic_pte_zeropage(struct mm_struct *dst_mm,
}
/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
-static int mfill_atomic_pte_continue(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
+static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
bool wp_copy)
@@ -269,7 +266,7 @@ static int mfill_atomic_pte_continue(struct mm_struct *dst_mm,
goto out_release;
}
- ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+ ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
page, false, wp_copy);
if (ret)
goto out_release;
@@ -310,7 +307,7 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
* mfill_atomic processing for HUGETLB vmas. Note that this routine is
* called with mmap_lock held, it will release mmap_lock before returning.
*/
-static __always_inline ssize_t mfill_atomic_hugetlb(struct mm_struct *dst_mm,
+static __always_inline ssize_t mfill_atomic_hugetlb(
struct vm_area_struct *dst_vma,
unsigned long dst_start,
unsigned long src_start,
@@ -318,6 +315,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(struct mm_struct *dst_mm,
enum mcopy_atomic_mode mode,
bool wp_copy)
{
+ struct mm_struct *dst_mm = dst_vma->vm_mm;
int vm_shared = dst_vma->vm_flags & VM_SHARED;
ssize_t err;
pte_t *dst_pte;
@@ -411,7 +409,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(struct mm_struct *dst_mm,
goto out_unlock;
}
- err = hugetlb_mfill_atomic_pte(dst_mm, dst_pte, dst_vma,
+ err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma,
dst_addr, src_addr, mode, &page,
wp_copy);
@@ -463,17 +461,15 @@ static __always_inline ssize_t mfill_atomic_hugetlb(struct mm_struct *dst_mm,
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
-extern ssize_t mfill_atomic_hugetlb(struct mm_struct *dst_mm,
- struct vm_area_struct *dst_vma,
- unsigned long dst_start,
- unsigned long src_start,
- unsigned long len,
- enum mcopy_atomic_mode mode,
- bool wp_copy);
+extern ssize_t mfill_atomic_hugetlb(struct vm_area_struct *dst_vma,
+ unsigned long dst_start,
+ unsigned long src_start,
+ unsigned long len,
+ enum mcopy_atomic_mode mode,
+ bool wp_copy);
#endif /* CONFIG_HUGETLB_PAGE */
-static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
+static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
@@ -484,7 +480,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
ssize_t err;
if (mode == MCOPY_ATOMIC_CONTINUE) {
- return mfill_atomic_pte_continue(dst_mm, dst_pmd, dst_vma,
+ return mfill_atomic_pte_continue(dst_pmd, dst_vma,
dst_addr, wp_copy);
}
@@ -500,14 +496,14 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
*/
if (!(dst_vma->vm_flags & VM_SHARED)) {
if (mode == MCOPY_ATOMIC_NORMAL)
- err = mfill_atomic_pte_copy(dst_mm, dst_pmd, dst_vma,
+ err = mfill_atomic_pte_copy(dst_pmd, dst_vma,
dst_addr, src_addr, page,
wp_copy);
else
- err = mfill_atomic_pte_zeropage(dst_mm, dst_pmd,
+ err = mfill_atomic_pte_zeropage(dst_pmd,
dst_vma, dst_addr);
} else {
- err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
+ err = shmem_mfill_atomic_pte(dst_pmd, dst_vma,
dst_addr, src_addr,
mode != MCOPY_ATOMIC_NORMAL,
wp_copy, page);
@@ -588,7 +584,7 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
* If this is a HUGETLB vma, pass off to appropriate routine
*/
if (is_vm_hugetlb_page(dst_vma))
- return mfill_atomic_hugetlb(dst_mm, dst_vma, dst_start,
+ return mfill_atomic_hugetlb(dst_vma, dst_start,
src_start, len, mcopy_mode,
wp_copy);
@@ -641,7 +637,7 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
BUG_ON(pmd_none(*dst_pmd));
BUG_ON(pmd_trans_huge(*dst_pmd));
- err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+ err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr,
src_addr, &page, mcopy_mode, wp_copy);
cond_resched();
@@ -710,7 +706,7 @@ ssize_t mfill_atomic_continue(struct mm_struct *dst_mm, unsigned long start,
mmap_changing, 0);
}
-long uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
+long uffd_wp_range(struct vm_area_struct *dst_vma,
unsigned long start, unsigned long len, bool enable_wp)
{
unsigned int mm_cp_flags;
@@ -730,7 +726,7 @@ long uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
*/
if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))
mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
- tlb_gather_mmu(&tlb, dst_mm);
+ tlb_gather_mmu(&tlb, dst_vma->vm_mm);
ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);
tlb_finish_mmu(&tlb);
@@ -782,7 +778,7 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
goto out_unlock;
}
- err = uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
+ err = uffd_wp_range(dst_vma, start, len, enable_wp);
/* Return 0 on success, <0 on failures */
if (err > 0)
--
2.40.0.rc0.216.gc4246ad0f0-googOn Mon, Mar 06, 2023 at 02:50:21PM -0800, Axel Rasmussen wrote: > Quite a few userfaultfd functions took both mm and vma pointers as > arguments. Since the mm is trivially accessible via vma->vm_mm, there's > no reason to pass both; it just needlessly extends the already long > argument list. > > Get rid of the mm pointer, where possible, to shorten the argument list. > > Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Peter Xu <peterx@redhat.com> One nit below: > @@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, > folio_in_pagecache = true; > } > > - ptl = huge_pte_lock(h, dst_mm, dst_pte); > + ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte); > > ret = -EIO; > if (folio_test_hwpoison(folio)) > @@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, > if (wp_copy) > _dst_pte = huge_pte_mkuffd_wp(_dst_pte); > > - set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); > + set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte); > > - hugetlb_count_add(pages_per_huge_page(h), dst_mm); > + hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm); When vm_mm referenced multiple times (say, >=3?), let's still cache it in a temp var? I'm not sure whether compiler is smart enough to already do that with a reg, even if so it may slightly improve readability too, imho, by avoiding the multiple but same indirection for the reader. Thanks, -- Peter Xu
> On Mar 6, 2023, at 5:03 PM, Peter Xu <peterx@redhat.com> wrote: > > !! External Email > > On Mon, Mar 06, 2023 at 02:50:21PM -0800, Axel Rasmussen wrote: >> Quite a few userfaultfd functions took both mm and vma pointers as >> arguments. Since the mm is trivially accessible via vma->vm_mm, there's >> no reason to pass both; it just needlessly extends the already long >> argument list. >> >> Get rid of the mm pointer, where possible, to shorten the argument list. >> >> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> > > Acked-by: Peter Xu <peterx@redhat.com> > > One nit below: > >> @@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, >> folio_in_pagecache = true; >> } >> >> - ptl = huge_pte_lock(h, dst_mm, dst_pte); >> + ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte); >> >> ret = -EIO; >> if (folio_test_hwpoison(folio)) >> @@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, >> if (wp_copy) >> _dst_pte = huge_pte_mkuffd_wp(_dst_pte); >> >> - set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); >> + set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte); >> >> - hugetlb_count_add(pages_per_huge_page(h), dst_mm); >> + hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm); > > When vm_mm referenced multiple times (say, >=3?), let's still cache it in a > temp var? > > I'm not sure whether compiler is smart enough to already do that with a > reg, even if so it may slightly improve readability too, imho, by avoiding > the multiple but same indirection for the reader. I am not sure if you referred to this code specifically or in general. I once looked into it, and the compiler is really stupid in this regard and super conservative when it comes to aliasing. Even if you use “restrict” keyword or “__pure” or “__const” function attributes, in certain cases (function calls to other compilation units, or inline assembly - I don’t remember) the compiler might ignore them. Worse, llvm and gcc are inconsistent. From code-generated perspective, I did not see a clear cut that benefits caching over not. From performance perspective the impact is negligible. I mention all of that because I thought it matters too, but it mostly does not. That’s all to say that in most cases, I think that whatever makes the code more readable should be preferred. I think that you are correct in saying that “caching” it will make the code more readable, but performance-wise it is probably meaningless.
On Tue, Mar 07, 2023 at 01:44:05AM +0000, Nadav Amit wrote: > > > > On Mar 6, 2023, at 5:03 PM, Peter Xu <peterx@redhat.com> wrote: > > > > !! External Email > > > > On Mon, Mar 06, 2023 at 02:50:21PM -0800, Axel Rasmussen wrote: > >> Quite a few userfaultfd functions took both mm and vma pointers as > >> arguments. Since the mm is trivially accessible via vma->vm_mm, there's > >> no reason to pass both; it just needlessly extends the already long > >> argument list. > >> > >> Get rid of the mm pointer, where possible, to shorten the argument list. > >> > >> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> > > > > Acked-by: Peter Xu <peterx@redhat.com> > > > > One nit below: > > > >> @@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, > >> folio_in_pagecache = true; > >> } > >> > >> - ptl = huge_pte_lock(h, dst_mm, dst_pte); > >> + ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte); > >> > >> ret = -EIO; > >> if (folio_test_hwpoison(folio)) > >> @@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm, > >> if (wp_copy) > >> _dst_pte = huge_pte_mkuffd_wp(_dst_pte); > >> > >> - set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); > >> + set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte); > >> > >> - hugetlb_count_add(pages_per_huge_page(h), dst_mm); > >> + hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm); > > > > When vm_mm referenced multiple times (say, >=3?), let's still cache it in a > > temp var? > > > > I'm not sure whether compiler is smart enough to already do that with a > > reg, even if so it may slightly improve readability too, imho, by avoiding > > the multiple but same indirection for the reader. > > I am not sure if you referred to this code specifically or in general. In general. IIRC there're more than one such case in this patch. > I once looked into it, and the compiler is really stupid in this regard > and super conservative when it comes to aliasing. Even if you use > “restrict” keyword or “__pure” or “__const” function attributes, in > certain cases (function calls to other compilation units, or inline > assembly - I don’t remember) the compiler might ignore them. Worse, llvm > and gcc are inconsistent. > > From code-generated perspective, I did not see a clear cut that benefits > caching over not. From performance perspective the impact is negligible. I > mention all of that because I thought it matters too, but it mostly does > not. > > That’s all to say that in most cases, I think that whatever makes the code > more readable should be preferred. I think that you are correct in saying > that “caching” it will make the code more readable, but performance-wise > it is probably meaningless. Thanks for the knowledge. I would suspect no matter how the output layout of the compilers will be the difference will be small. I prefer it more for readability as you said but not strongly either way. -- Peter Xu
© 2016 - 2026 Red Hat, Inc.