| Message ID | 20210308112809.26107-6-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Some cleanups for hugetlb | expand |
On 3/8/21 3:28 AM, Miaohe Lin wrote: > The fault_mutex hashing overhead can be avoided in truncate_op case because > page faults can not race with truncation in this routine. So calculate hash > for fault_mutex only in !truncate_op case to save some cpu cycles. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > fs/hugetlbfs/inode.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index c262566f7c5d..d81f52b87bd7 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, > > for (i = 0; i < pagevec_count(&pvec); ++i) { > struct page *page = pvec.pages[i]; > - u32 hash; > + u32 hash = 0; Do we need to initialize hash here? I would not bring this up normally, but the purpose of the patch is to save cpu cycles.
Hi: On 2021/3/13 4:03, Mike Kravetz wrote: > On 3/8/21 3:28 AM, Miaohe Lin wrote: >> The fault_mutex hashing overhead can be avoided in truncate_op case because >> page faults can not race with truncation in this routine. So calculate hash >> for fault_mutex only in !truncate_op case to save some cpu cycles. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> fs/hugetlbfs/inode.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >> index c262566f7c5d..d81f52b87bd7 100644 >> --- a/fs/hugetlbfs/inode.c >> +++ b/fs/hugetlbfs/inode.c >> @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, >> >> for (i = 0; i < pagevec_count(&pvec); ++i) { >> struct page *page = pvec.pages[i]; >> - u32 hash; >> + u32 hash = 0; > > Do we need to initialize hash here? > I would not bring this up normally, but the purpose of the patch is to save > cpu cycles. The hash is initialized here in order to avoid false positive "uninitialized local variable used" warning. Or this is indeed unnecessary? Many thanks for review. >
On 3/12/21 6:49 PM, Miaohe Lin wrote: > Hi: > On 2021/3/13 4:03, Mike Kravetz wrote: >> On 3/8/21 3:28 AM, Miaohe Lin wrote: >>> The fault_mutex hashing overhead can be avoided in truncate_op case because >>> page faults can not race with truncation in this routine. So calculate hash >>> for fault_mutex only in !truncate_op case to save some cpu cycles. >>> >>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>> --- >>> fs/hugetlbfs/inode.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >>> index c262566f7c5d..d81f52b87bd7 100644 >>> --- a/fs/hugetlbfs/inode.c >>> +++ b/fs/hugetlbfs/inode.c >>> @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, >>> >>> for (i = 0; i < pagevec_count(&pvec); ++i) { >>> struct page *page = pvec.pages[i]; >>> - u32 hash; >>> + u32 hash = 0; >> >> Do we need to initialize hash here? >> I would not bring this up normally, but the purpose of the patch is to save >> cpu cycles. > > The hash is initialized here in order to avoid false positive > "uninitialized local variable used" warning. Or this is indeed unnecessary? > Of course. In this case we know more about usage then the compiler. You can add: Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
On 2021/3/14 5:17, Mike Kravetz wrote: > On 3/12/21 6:49 PM, Miaohe Lin wrote: >> Hi: >> On 2021/3/13 4:03, Mike Kravetz wrote: >>> On 3/8/21 3:28 AM, Miaohe Lin wrote: >>>> The fault_mutex hashing overhead can be avoided in truncate_op case because >>>> page faults can not race with truncation in this routine. So calculate hash >>>> for fault_mutex only in !truncate_op case to save some cpu cycles. >>>> >>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>>> --- >>>> fs/hugetlbfs/inode.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >>>> index c262566f7c5d..d81f52b87bd7 100644 >>>> --- a/fs/hugetlbfs/inode.c >>>> +++ b/fs/hugetlbfs/inode.c >>>> @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, >>>> >>>> for (i = 0; i < pagevec_count(&pvec); ++i) { >>>> struct page *page = pvec.pages[i]; >>>> - u32 hash; >>>> + u32 hash = 0; >>> >>> Do we need to initialize hash here? >>> I would not bring this up normally, but the purpose of the patch is to save >>> cpu cycles. >> >> The hash is initialized here in order to avoid false positive >> "uninitialized local variable used" warning. Or this is indeed unnecessary? >> > > Of course. In this case we know more about usage then the compiler. > You can add: > I see. Many thanks. Am I supposed to resend the whole v2 patch series ? Or just a single v2 patch with change mentioned above? Please let me know which is the easiest one for you. > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> >
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index c262566f7c5d..d81f52b87bd7 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, for (i = 0; i < pagevec_count(&pvec); ++i) { struct page *page = pvec.pages[i]; - u32 hash; + u32 hash = 0; index = page->index; - hash = hugetlb_fault_mutex_hash(mapping, index); if (!truncate_op) { /* * Only need to hold the fault mutex in the @@ -493,6 +492,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, * page faults. Races are not possible in the * case of truncation. */ + hash = hugetlb_fault_mutex_hash(mapping, index); mutex_lock(&hugetlb_fault_mutex_table[hash]); }
The fault_mutex hashing overhead can be avoided in truncate_op case because page faults can not race with truncation in this routine. So calculate hash for fault_mutex only in !truncate_op case to save some cpu cycles. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- fs/hugetlbfs/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)