| Message ID | 20230515172608.3558391-1-yuanchu@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: pagemap: restrict pagewalk to the requested range | expand |
On Tue, May 16, 2023 at 01:26:08AM +0800, Yuanchu Xie wrote: > The pagewalk in pagemap_read reads one PTE past the end of the requested > range, and stops when the buffer runs out of space. While it produces > the right result, the extra read is unnecessary and less performant. > > I timed the following command before and after this patch: > dd count=100000 if=/proc/self/pagemap of=/dev/null > The results are consistently within 0.001s across 5 runs. > > Before: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s > > real 0m0.078s > user 0m0.012s > sys 0m0.065s > > After: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s > > real 0m0.050s > user 0m0.011s > sys 0m0.039s > > Signed-off-by: Yuanchu Xie <yuanchu@google.com> Acked-by: Peter Xu <peterx@redhat.com>
On Tue, May 16, 2023 at 01:26:08AM +0800, Yuanchu Xie wrote: > The pagewalk in pagemap_read reads one PTE past the end of the requested > range, and stops when the buffer runs out of space. While it produces > the right result, the extra read is unnecessary and less performant. > > I timed the following command before and after this patch: > dd count=100000 if=/proc/self/pagemap of=/dev/null > The results are consistently within 0.001s across 5 runs. > > Before: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s > > real 0m0.078s > user 0m0.012s > sys 0m0.065s > > After: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s > > real 0m0.050s > user 0m0.011s > sys 0m0.039s > > Signed-off-by: Yuanchu Xie <yuanchu@google.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> > --- > fs/proc/task_mmu.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 420510f6a545..6259dd432eeb 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1689,23 +1689,23 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, > /* watch out for wraparound */ > start_vaddr = end_vaddr; > if (svpfn <= (ULONG_MAX >> PAGE_SHIFT)) { > + unsigned long end; > + > ret = mmap_read_lock_killable(mm); > if (ret) > goto out_free; > start_vaddr = untagged_addr_remote(mm, svpfn << PAGE_SHIFT); > mmap_read_unlock(mm); > + > + end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT); > + if (end >= start_vaddr && end < mm->task_size) > + end_vaddr = end; > } > > /* Ensure the address is inside the task */ > if (start_vaddr > mm->task_size) > start_vaddr = end_vaddr; > > - /* > - * The odds are that this will stop walking way > - * before end_vaddr, because the length of the > - * user buffer is tracked in "pm", and the walk > - * will stop when we hit the end of the buffer. > - */ > ret = 0; > while (count && (start_vaddr < end_vaddr)) { > int len; > -- > 2.40.1.606.ga4b1b128d6-goog > >
On Mon, May 15, 2023 at 10:26 AM Yuanchu Xie <yuanchu@google.com> wrote: > > The pagewalk in pagemap_read reads one PTE past the end of the requested > range, and stops when the buffer runs out of space. While it produces > the right result, the extra read is unnecessary and less performant. > > I timed the following command before and after this patch: > dd count=100000 if=/proc/self/pagemap of=/dev/null > The results are consistently within 0.001s across 5 runs. > > Before: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s > > real 0m0.078s > user 0m0.012s > sys 0m0.065s > > After: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s > > real 0m0.050s > user 0m0.011s > sys 0m0.039s > > Signed-off-by: Yuanchu Xie <yuanchu@google.com> Reviewed-by: Yang Shi <shy828301@gmail.com> > --- > fs/proc/task_mmu.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 420510f6a545..6259dd432eeb 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1689,23 +1689,23 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, > /* watch out for wraparound */ > start_vaddr = end_vaddr; > if (svpfn <= (ULONG_MAX >> PAGE_SHIFT)) { > + unsigned long end; > + > ret = mmap_read_lock_killable(mm); > if (ret) > goto out_free; > start_vaddr = untagged_addr_remote(mm, svpfn << PAGE_SHIFT); > mmap_read_unlock(mm); > + > + end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT); > + if (end >= start_vaddr && end < mm->task_size) > + end_vaddr = end; > } > > /* Ensure the address is inside the task */ > if (start_vaddr > mm->task_size) > start_vaddr = end_vaddr; > > - /* > - * The odds are that this will stop walking way > - * before end_vaddr, because the length of the > - * user buffer is tracked in "pm", and the walk > - * will stop when we hit the end of the buffer. > - */ > ret = 0; > while (count && (start_vaddr < end_vaddr)) { > int len; > -- > 2.40.1.606.ga4b1b128d6-goog >
On Tue, 16 May 2023, Yuanchu Xie wrote: > The pagewalk in pagemap_read reads one PTE past the end of the requested > range, and stops when the buffer runs out of space. While it produces > the right result, the extra read is unnecessary and less performant. > > I timed the following command before and after this patch: > dd count=100000 if=/proc/self/pagemap of=/dev/null > The results are consistently within 0.001s across 5 runs. > > Before: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s > > real 0m0.078s > user 0m0.012s > sys 0m0.065s > > After: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s > > real 0m0.050s > user 0m0.011s > sys 0m0.039s > > Signed-off-by: Yuanchu Xie <yuanchu@google.com> Acked-by: David Rientjes <rientjes@google.com>
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 420510f6a545..6259dd432eeb 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1689,23 +1689,23 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, /* watch out for wraparound */ start_vaddr = end_vaddr; if (svpfn <= (ULONG_MAX >> PAGE_SHIFT)) { + unsigned long end; + ret = mmap_read_lock_killable(mm); if (ret) goto out_free; start_vaddr = untagged_addr_remote(mm, svpfn << PAGE_SHIFT); mmap_read_unlock(mm); + + end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT); + if (end >= start_vaddr && end < mm->task_size) + end_vaddr = end; } /* Ensure the address is inside the task */ if (start_vaddr > mm->task_size) start_vaddr = end_vaddr; - /* - * The odds are that this will stop walking way - * before end_vaddr, because the length of the - * user buffer is tracked in "pm", and the walk - * will stop when we hit the end of the buffer. - */ ret = 0; while (count && (start_vaddr < end_vaddr)) { int len;
The pagewalk in pagemap_read reads one PTE past the end of the requested range, and stops when the buffer runs out of space. While it produces the right result, the extra read is unnecessary and less performant. I timed the following command before and after this patch: dd count=100000 if=/proc/self/pagemap of=/dev/null The results are consistently within 0.001s across 5 runs. Before: 100000+0 records in 100000+0 records out 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s real 0m0.078s user 0m0.012s sys 0m0.065s After: 100000+0 records in 100000+0 records out 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s real 0m0.050s user 0m0.011s sys 0m0.039s Signed-off-by: Yuanchu Xie <yuanchu@google.com> --- fs/proc/task_mmu.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)