| Message ID | 20240520105525.2176322-1-xu.yang_2@nxp.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] iomap: avoid redundant fault_in_iov_iter_readable() judgement when use larger chunks | expand |
On Mon, May 20, 2024 at 06:55:25PM +0800, Xu Yang wrote: > Since commit (5d8edfb900d5 "iomap: Copy larger chunks from userspace"), > iomap will try to copy in larger chunks than PAGE_SIZE. However, if the > mapping doesn't support large folio, only one page of maximum 4KB will > be created and 4KB data will be writen to pagecache each time. Then, > next 4KB will be handled in next iteration. This will cause potential > write performance problem. > > If chunk is 2MB, total 512 pages need to be handled finally. During this > period, fault_in_iov_iter_readable() is called to check iov_iter readable > validity. Since only 4KB will be handled each time, below address space > will be checked over and over again: > > start end > - > buf, buf+2MB > buf+4KB, buf+2MB > buf+8KB, buf+2MB > ... > buf+2044KB buf+2MB > > Obviously the checking size is wrong since only 4KB will be handled each > time. So this will get a correct chunk to let iomap work well in non-large > folio case. > > With this change, the write speed will be stable. Tested on ARM64 device. > > Before: > > - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (334 MB/s) > - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (278 MB/s) > - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (204 MB/s) > - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (170 MB/s) > - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (150 MB/s) > - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (139 MB/s) > > After: > > - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (339 MB/s) > - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (330 MB/s) > - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (332 MB/s) > - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (333 MB/s) > - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (333 MB/s) > - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (333 MB/s) > > Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") > Cc: stable@vger.kernel.org > Signed-off-by: Xu Yang <xu.yang_2@nxp.com> > > --- > Changes in v2: > - fix address space description in message > Changes in v3: > - adjust 'chunk' and add mapping_max_folio_size() in header file > as suggested by Matthew > - add write performance results in commit message > --- > fs/iomap/buffered-io.c | 2 +- > include/linux/pagemap.h | 37 ++++++++++++++++++++++++------------- > 2 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index 41c8f0c68ef5..c5802a459334 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -898,11 +898,11 @@ static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len, > static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) > { > loff_t length = iomap_length(iter); > - size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER; > loff_t pos = iter->pos; > ssize_t total_written = 0; > long status = 0; > struct address_space *mapping = iter->inode->i_mapping; > + size_t chunk = mapping_max_folio_size(mapping); > unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0; > > do { > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index c5e33e2ca48a..6be8e22360f1 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -346,6 +346,19 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask) > m->gfp_mask = mask; > } > > +/* > + * There are some parts of the kernel which assume that PMD entries > + * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > + * limit the maximum allocation order to PMD size. I'm not aware of any > + * assumptions about maximum order if THP are disabled, but 8 seems like > + * a good order (that's 1MB if you're using 4kB pages) > + */ > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > +#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > +#else > +#define MAX_PAGECACHE_ORDER 8 > +#endif > + > /** > * mapping_set_large_folios() - Indicate the file supports large folios. > * @mapping: The file. > @@ -372,6 +385,17 @@ static inline bool mapping_large_folio_support(struct address_space *mapping) > test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); > } > > +/* > + * Get max folio size in case of supporting large folio, otherwise return > + * PAGE_SIZE. Minor quibble -- the comment doesn't need to restate what the function does because we can see that in the code below. /* Return the maximum folio size for this pagecache mapping, in bytes. */ With that fixed, Reviewed-by: Darrick J. Wong <djwong@kernel.org> --D > + */ > +static inline size_t mapping_max_folio_size(struct address_space *mapping) > +{ > + if (mapping_large_folio_support(mapping)) > + return PAGE_SIZE << MAX_PAGECACHE_ORDER; > + return PAGE_SIZE; > +} > + > static inline int filemap_nr_thps(struct address_space *mapping) > { > #ifdef CONFIG_READ_ONLY_THP_FOR_FS > @@ -530,19 +554,6 @@ static inline void *detach_page_private(struct page *page) > return folio_detach_private(page_folio(page)); > } > > -/* > - * There are some parts of the kernel which assume that PMD entries > - * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > - * limit the maximum allocation order to PMD size. I'm not aware of any > - * assumptions about maximum order if THP are disabled, but 8 seems like > - * a good order (that's 1MB if you're using 4kB pages) > - */ > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > -#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > -#else > -#define MAX_PAGECACHE_ORDER 8 > -#endif > - > #ifdef CONFIG_NUMA > struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order); > #else > -- > 2.34.1 > >
This looks generally good. But a few nitpicks: - please split the mapping_max_folio_size addition into a separate well-documented helper instead of merging it into the iomap change. - judgment is a really weird term for code. Here is a subject I came up with, which might not be perfect: "iomap: fault in smaller chunks for non-large folio mappings"
On Mon, May 20, 2024 at 08:08:23AM -0700, Darrick J. Wong wrote: > On Mon, May 20, 2024 at 06:55:25PM +0800, Xu Yang wrote: > > Since commit (5d8edfb900d5 "iomap: Copy larger chunks from userspace"), > > iomap will try to copy in larger chunks than PAGE_SIZE. However, if the > > mapping doesn't support large folio, only one page of maximum 4KB will > > be created and 4KB data will be writen to pagecache each time. Then, > > next 4KB will be handled in next iteration. This will cause potential > > write performance problem. > > > > If chunk is 2MB, total 512 pages need to be handled finally. During this > > period, fault_in_iov_iter_readable() is called to check iov_iter readable > > validity. Since only 4KB will be handled each time, below address space > > will be checked over and over again: > > > > start end > > - > > buf, buf+2MB > > buf+4KB, buf+2MB > > buf+8KB, buf+2MB > > ... > > buf+2044KB buf+2MB > > > > Obviously the checking size is wrong since only 4KB will be handled each > > time. So this will get a correct chunk to let iomap work well in non-large > > folio case. > > > > With this change, the write speed will be stable. Tested on ARM64 device. > > > > Before: > > > > - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (334 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (278 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (204 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (170 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (150 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (139 MB/s) > > > > After: > > > > - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (339 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (330 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (332 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (333 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (333 MB/s) > > - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (333 MB/s) > > > > Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") > > Cc: stable@vger.kernel.org > > Signed-off-by: Xu Yang <xu.yang_2@nxp.com> > > > > --- > > Changes in v2: > > - fix address space description in message > > Changes in v3: > > - adjust 'chunk' and add mapping_max_folio_size() in header file > > as suggested by Matthew > > - add write performance results in commit message > > --- > > fs/iomap/buffered-io.c | 2 +- > > include/linux/pagemap.h | 37 ++++++++++++++++++++++++------------- > > 2 files changed, 25 insertions(+), 14 deletions(-) > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > index 41c8f0c68ef5..c5802a459334 100644 > > --- a/fs/iomap/buffered-io.c > > +++ b/fs/iomap/buffered-io.c > > @@ -898,11 +898,11 @@ static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len, > > static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) > > { > > loff_t length = iomap_length(iter); > > - size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER; > > loff_t pos = iter->pos; > > ssize_t total_written = 0; > > long status = 0; > > struct address_space *mapping = iter->inode->i_mapping; > > + size_t chunk = mapping_max_folio_size(mapping); > > unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0; > > > > do { > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > > index c5e33e2ca48a..6be8e22360f1 100644 > > --- a/include/linux/pagemap.h > > +++ b/include/linux/pagemap.h > > @@ -346,6 +346,19 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask) > > m->gfp_mask = mask; > > } > > > > +/* > > + * There are some parts of the kernel which assume that PMD entries > > + * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > > + * limit the maximum allocation order to PMD size. I'm not aware of any > > + * assumptions about maximum order if THP are disabled, but 8 seems like > > + * a good order (that's 1MB if you're using 4kB pages) > > + */ > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > +#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > > +#else > > +#define MAX_PAGECACHE_ORDER 8 > > +#endif > > + > > /** > > * mapping_set_large_folios() - Indicate the file supports large folios. > > * @mapping: The file. > > @@ -372,6 +385,17 @@ static inline bool mapping_large_folio_support(struct address_space *mapping) > > test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); > > } > > > > +/* > > + * Get max folio size in case of supporting large folio, otherwise return > > + * PAGE_SIZE. > > Minor quibble -- the comment doesn't need to restate what the function > does because we can see that in the code below. > > /* Return the maximum folio size for this pagecache mapping, in bytes. */ > > With that fixed, > Reviewed-by: Darrick J. Wong <djwong@kernel.org> > Okay, will change the comment in v4. Thanks, Xu Yang > --D > > > > + */ > > +static inline size_t mapping_max_folio_size(struct address_space *mapping) > > +{ > > + if (mapping_large_folio_support(mapping)) > > + return PAGE_SIZE << MAX_PAGECACHE_ORDER; > > + return PAGE_SIZE; > > +} > > + > > static inline int filemap_nr_thps(struct address_space *mapping) > > { > > #ifdef CONFIG_READ_ONLY_THP_FOR_FS > > @@ -530,19 +554,6 @@ static inline void *detach_page_private(struct page *page) > > return folio_detach_private(page_folio(page)); > > } > > > > -/* > > - * There are some parts of the kernel which assume that PMD entries > > - * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, > > - * limit the maximum allocation order to PMD size. I'm not aware of any > > - * assumptions about maximum order if THP are disabled, but 8 seems like > > - * a good order (that's 1MB if you're using 4kB pages) > > - */ > > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > -#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER > > -#else > > -#define MAX_PAGECACHE_ORDER 8 > > -#endif > > - > > #ifdef CONFIG_NUMA > > struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order); > > #else > > -- > > 2.34.1 > > > >
On Mon, May 20, 2024 at 05:29:17PM +0200, Christoph Hellwig wrote: > This looks generally good. But a few nitpicks: > > - please split the mapping_max_folio_size addition into a separate > well-documented helper instead of merging it into the iomap change. Okay. Will do that in v4. > - judgment is a really weird term for code. Here is a subject I came > up with, which might not be perfect: > > "iomap: fault in smaller chunks for non-large folio mappings" > A better choice for me. Thanks, Xu Yang
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 41c8f0c68ef5..c5802a459334 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -898,11 +898,11 @@ static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len, static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) { loff_t length = iomap_length(iter); - size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER; loff_t pos = iter->pos; ssize_t total_written = 0; long status = 0; struct address_space *mapping = iter->inode->i_mapping; + size_t chunk = mapping_max_folio_size(mapping); unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0; do { diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index c5e33e2ca48a..6be8e22360f1 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -346,6 +346,19 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask) m->gfp_mask = mask; } +/* + * There are some parts of the kernel which assume that PMD entries + * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, + * limit the maximum allocation order to PMD size. I'm not aware of any + * assumptions about maximum order if THP are disabled, but 8 seems like + * a good order (that's 1MB if you're using 4kB pages) + */ +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER +#else +#define MAX_PAGECACHE_ORDER 8 +#endif + /** * mapping_set_large_folios() - Indicate the file supports large folios. * @mapping: The file. @@ -372,6 +385,17 @@ static inline bool mapping_large_folio_support(struct address_space *mapping) test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); } +/* + * Get max folio size in case of supporting large folio, otherwise return + * PAGE_SIZE. + */ +static inline size_t mapping_max_folio_size(struct address_space *mapping) +{ + if (mapping_large_folio_support(mapping)) + return PAGE_SIZE << MAX_PAGECACHE_ORDER; + return PAGE_SIZE; +} + static inline int filemap_nr_thps(struct address_space *mapping) { #ifdef CONFIG_READ_ONLY_THP_FOR_FS @@ -530,19 +554,6 @@ static inline void *detach_page_private(struct page *page) return folio_detach_private(page_folio(page)); } -/* - * There are some parts of the kernel which assume that PMD entries - * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, - * limit the maximum allocation order to PMD size. I'm not aware of any - * assumptions about maximum order if THP are disabled, but 8 seems like - * a good order (that's 1MB if you're using 4kB pages) - */ -#ifdef CONFIG_TRANSPARENT_HUGEPAGE -#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER -#else -#define MAX_PAGECACHE_ORDER 8 -#endif - #ifdef CONFIG_NUMA struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order); #else
Since commit (5d8edfb900d5 "iomap: Copy larger chunks from userspace"), iomap will try to copy in larger chunks than PAGE_SIZE. However, if the mapping doesn't support large folio, only one page of maximum 4KB will be created and 4KB data will be writen to pagecache each time. Then, next 4KB will be handled in next iteration. This will cause potential write performance problem. If chunk is 2MB, total 512 pages need to be handled finally. During this period, fault_in_iov_iter_readable() is called to check iov_iter readable validity. Since only 4KB will be handled each time, below address space will be checked over and over again: start end - buf, buf+2MB buf+4KB, buf+2MB buf+8KB, buf+2MB ... buf+2044KB buf+2MB Obviously the checking size is wrong since only 4KB will be handled each time. So this will get a correct chunk to let iomap work well in non-large folio case. With this change, the write speed will be stable. Tested on ARM64 device. Before: - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (334 MB/s) - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (278 MB/s) - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (204 MB/s) - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (170 MB/s) - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (150 MB/s) - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (139 MB/s) After: - dd if=/dev/zero of=/dev/sda bs=400K count=10485 (339 MB/s) - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (330 MB/s) - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (332 MB/s) - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (333 MB/s) - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (333 MB/s) - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (333 MB/s) Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") Cc: stable@vger.kernel.org Signed-off-by: Xu Yang <xu.yang_2@nxp.com> --- Changes in v2: - fix address space description in message Changes in v3: - adjust 'chunk' and add mapping_max_folio_size() in header file as suggested by Matthew - add write performance results in commit message --- fs/iomap/buffered-io.c | 2 +- include/linux/pagemap.h | 37 ++++++++++++++++++++++++------------- 2 files changed, 25 insertions(+), 14 deletions(-)