| Message ID | 20240213215520.1048625-7-zi.yan@sent.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Split a folio to any lower order folios | expand |
On 13/02/2024 21:55, Zi Yan wrote: > From: Zi Yan <ziy@nvidia.com> > > To minimize the number of pages after a huge page truncation, we do not > need to split it all the way down to order-0. The huge page has at most > three parts, the part before offset, the part to be truncated, the part > remaining at the end. Find the greatest common divisor of them to > calculate the new page order from it, so we can split the huge > page to this order and keep the remaining pages as large and as few as > possible. > > Signed-off-by: Zi Yan <ziy@nvidia.com> > --- > mm/truncate.c | 21 +++++++++++++++++++-- > 1 file changed, 19 insertions(+), 2 deletions(-) > > diff --git a/mm/truncate.c b/mm/truncate.c > index 725b150e47ac..49ddbbf7a617 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -21,6 +21,7 @@ > #include <linux/task_io_accounting_ops.h> > #include <linux/shmem_fs.h> > #include <linux/rmap.h> > +#include <linux/gcd.h> > #include "internal.h" > > /* > @@ -210,7 +211,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) > bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) > { > loff_t pos = folio_pos(folio); > - unsigned int offset, length; > + unsigned int offset, length, remaining; > + unsigned int new_order = folio_order(folio); > > if (pos < start) > offset = start - pos; > @@ -221,6 +223,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) > length = length - offset; > else > length = end + 1 - pos - offset; > + remaining = folio_size(folio) - offset - length; > > folio_wait_writeback(folio); > if (length == folio_size(folio)) { > @@ -235,11 +238,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) > */ > folio_zero_range(folio, offset, length); > > + /* > + * Use the greatest common divisor of offset, length, and remaining > + * as the smallest page size and compute the new order from it. So we > + * can truncate a subpage as large as possible. Round up gcd to > + * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0. > + */ > + new_order = ilog2(round_up(gcd(gcd(offset, length), remaining), > + PAGE_SIZE) / PAGE_SIZE); Given you have up to 2 regions remaining, isn't it possible that you want a different order for both those regions (or even multiple orders within the same region)? I guess you just choose gcd for simplicity? > + > + /* order-1 THP not supported, downgrade to order-0 */ > + if (new_order == 1) > + new_order = 0; I guess this would need to change if supporting order-1 file folios? > + > + > if (folio_has_private(folio)) > folio_invalidate(folio, offset, length); > if (!folio_test_large(folio)) > return true; > - if (split_folio(folio) == 0) > + if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0) I know you are discussing removing this patch, but since you created split_folio_to_order() wouldn't that be better here? Thanks, Ryan > return true; > if (folio_test_dirty(folio)) > return false;
On 14 Feb 2024, at 5:43, Ryan Roberts wrote: > On 13/02/2024 21:55, Zi Yan wrote: >> From: Zi Yan <ziy@nvidia.com> >> >> To minimize the number of pages after a huge page truncation, we do not >> need to split it all the way down to order-0. The huge page has at most >> three parts, the part before offset, the part to be truncated, the part >> remaining at the end. Find the greatest common divisor of them to >> calculate the new page order from it, so we can split the huge >> page to this order and keep the remaining pages as large and as few as >> possible. >> >> Signed-off-by: Zi Yan <ziy@nvidia.com> >> --- >> mm/truncate.c | 21 +++++++++++++++++++-- >> 1 file changed, 19 insertions(+), 2 deletions(-) >> >> diff --git a/mm/truncate.c b/mm/truncate.c >> index 725b150e47ac..49ddbbf7a617 100644 >> --- a/mm/truncate.c >> +++ b/mm/truncate.c >> @@ -21,6 +21,7 @@ >> #include <linux/task_io_accounting_ops.h> >> #include <linux/shmem_fs.h> >> #include <linux/rmap.h> >> +#include <linux/gcd.h> >> #include "internal.h" >> >> /* >> @@ -210,7 +211,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) >> bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >> { >> loff_t pos = folio_pos(folio); >> - unsigned int offset, length; >> + unsigned int offset, length, remaining; >> + unsigned int new_order = folio_order(folio); >> >> if (pos < start) >> offset = start - pos; >> @@ -221,6 +223,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >> length = length - offset; >> else >> length = end + 1 - pos - offset; >> + remaining = folio_size(folio) - offset - length; >> >> folio_wait_writeback(folio); >> if (length == folio_size(folio)) { >> @@ -235,11 +238,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >> */ >> folio_zero_range(folio, offset, length); >> >> + /* >> + * Use the greatest common divisor of offset, length, and remaining >> + * as the smallest page size and compute the new order from it. So we >> + * can truncate a subpage as large as possible. Round up gcd to >> + * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0. >> + */ >> + new_order = ilog2(round_up(gcd(gcd(offset, length), remaining), >> + PAGE_SIZE) / PAGE_SIZE); > > Given you have up to 2 regions remaining, isn't it possible that you want a > different order for both those regions (or even multiple orders within the same > region)? I guess you just choose gcd for simplicity? Right. You raise the same concern as Hugh[1]. I am minimizing the call of split_huge_page_to_list_to_order() and you and Hugh want to minimize the number of folios after the split. Yours will give better outcome after split, but requires either multiple calls or a more sophisticated implementation of page split[2]. We probably can revisit this once splitting to any order gets wider use. >> + >> + /* order-1 THP not supported, downgrade to order-0 */ >> + if (new_order == 1) >> + new_order = 0; > > I guess this would need to change if supporting order-1 file folios? Right. >> + >> + >> if (folio_has_private(folio)) >> folio_invalidate(folio, offset, length); >> if (!folio_test_large(folio)) >> return true; >> - if (split_folio(folio) == 0) >> + if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0) > > I know you are discussing removing this patch, but since you created > split_folio_to_order() wouldn't that be better here? Sure. Will change the patch locally. [1] https://lore.kernel.org/linux-mm/9dd96da-efa2-5123-20d4-4992136ef3ad@google.com/ [2] https://lore.kernel.org/linux-mm/0AC0520E-1BD2-497E-A7ED-05394400BFC9@nvidia.com/ -- Best Regards, Yan, Zi
On 14/02/2024 16:19, Zi Yan wrote: > On 14 Feb 2024, at 5:43, Ryan Roberts wrote: > >> On 13/02/2024 21:55, Zi Yan wrote: >>> From: Zi Yan <ziy@nvidia.com> >>> >>> To minimize the number of pages after a huge page truncation, we do not >>> need to split it all the way down to order-0. The huge page has at most >>> three parts, the part before offset, the part to be truncated, the part >>> remaining at the end. Find the greatest common divisor of them to >>> calculate the new page order from it, so we can split the huge >>> page to this order and keep the remaining pages as large and as few as >>> possible. >>> >>> Signed-off-by: Zi Yan <ziy@nvidia.com> >>> --- >>> mm/truncate.c | 21 +++++++++++++++++++-- >>> 1 file changed, 19 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/truncate.c b/mm/truncate.c >>> index 725b150e47ac..49ddbbf7a617 100644 >>> --- a/mm/truncate.c >>> +++ b/mm/truncate.c >>> @@ -21,6 +21,7 @@ >>> #include <linux/task_io_accounting_ops.h> >>> #include <linux/shmem_fs.h> >>> #include <linux/rmap.h> >>> +#include <linux/gcd.h> >>> #include "internal.h" >>> >>> /* >>> @@ -210,7 +211,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) >>> bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> { >>> loff_t pos = folio_pos(folio); >>> - unsigned int offset, length; >>> + unsigned int offset, length, remaining; >>> + unsigned int new_order = folio_order(folio); >>> >>> if (pos < start) >>> offset = start - pos; >>> @@ -221,6 +223,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> length = length - offset; >>> else >>> length = end + 1 - pos - offset; >>> + remaining = folio_size(folio) - offset - length; >>> >>> folio_wait_writeback(folio); >>> if (length == folio_size(folio)) { >>> @@ -235,11 +238,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> */ >>> folio_zero_range(folio, offset, length); >>> >>> + /* >>> + * Use the greatest common divisor of offset, length, and remaining >>> + * as the smallest page size and compute the new order from it. So we >>> + * can truncate a subpage as large as possible. Round up gcd to >>> + * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0. >>> + */ >>> + new_order = ilog2(round_up(gcd(gcd(offset, length), remaining), >>> + PAGE_SIZE) / PAGE_SIZE); >> >> Given you have up to 2 regions remaining, isn't it possible that you want a >> different order for both those regions (or even multiple orders within the same >> region)? I guess you just choose gcd for simplicity? > > Right. You raise the same concern as Hugh[1]. I am minimizing the call of > split_huge_page_to_list_to_order() and you and Hugh want to minimize the > number of folios after the split. Yours will give better outcome after split, > but requires either multiple calls or a more sophisticated implementation > of page split[2]. We probably can revisit this once splitting to any order > gets wider use. Yeah, fair enough. Sorry hadn't read Hugh's original feedback. > >>> + >>> + /* order-1 THP not supported, downgrade to order-0 */ >>> + if (new_order == 1) >>> + new_order = 0; >> >> I guess this would need to change if supporting order-1 file folios? > > Right. > >>> + >>> + >>> if (folio_has_private(folio)) >>> folio_invalidate(folio, offset, length); >>> if (!folio_test_large(folio)) >>> return true; >>> - if (split_folio(folio) == 0) >>> + if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0) >> >> I know you are discussing removing this patch, but since you created >> split_folio_to_order() wouldn't that be better here? > > Sure. Will change the patch locally. > > [1] https://lore.kernel.org/linux-mm/9dd96da-efa2-5123-20d4-4992136ef3ad@google.com/ > [2] https://lore.kernel.org/linux-mm/0AC0520E-1BD2-497E-A7ED-05394400BFC9@nvidia.com/ > > -- > Best Regards, > Yan, Zi
diff --git a/mm/truncate.c b/mm/truncate.c index 725b150e47ac..49ddbbf7a617 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -21,6 +21,7 @@ #include <linux/task_io_accounting_ops.h> #include <linux/shmem_fs.h> #include <linux/rmap.h> +#include <linux/gcd.h> #include "internal.h" /* @@ -210,7 +211,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) { loff_t pos = folio_pos(folio); - unsigned int offset, length; + unsigned int offset, length, remaining; + unsigned int new_order = folio_order(folio); if (pos < start) offset = start - pos; @@ -221,6 +223,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) length = length - offset; else length = end + 1 - pos - offset; + remaining = folio_size(folio) - offset - length; folio_wait_writeback(folio); if (length == folio_size(folio)) { @@ -235,11 +238,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) */ folio_zero_range(folio, offset, length); + /* + * Use the greatest common divisor of offset, length, and remaining + * as the smallest page size and compute the new order from it. So we + * can truncate a subpage as large as possible. Round up gcd to + * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0. + */ + new_order = ilog2(round_up(gcd(gcd(offset, length), remaining), + PAGE_SIZE) / PAGE_SIZE); + + /* order-1 THP not supported, downgrade to order-0 */ + if (new_order == 1) + new_order = 0; + + if (folio_has_private(folio)) folio_invalidate(folio, offset, length); if (!folio_test_large(folio)) return true; - if (split_folio(folio) == 0) + if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0) return true; if (folio_test_dirty(folio)) return false;