| Message ID | 20190905182348.5319-4-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Large pages in the page cache | expand |
On Fri, Sep 06, 2019 at 06:04:05AM +0800, kbuild test robot wrote: > Hi Matthew, > > Thank you for the patch! Yet something to improve: > > [auto build test ERROR on linus/master] > [cannot apply to v5.3-rc7 next-20190904] > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] It looks like you're not applying these to the -mm tree? I thought that was included in -next.
On Thu, Sep 05, 2019 at 11:23:48AM -0700, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > Add FGP_PMD to indicate that we're trying to find-or-create a page that > is at least PMD_ORDER in size. The internal 'conflict' entry usage > is modelled after that in DAX, but the implementations are different > due to DAX using multi-order entries and the page cache using multiple > order-0 entries. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > include/linux/pagemap.h | 9 +++++ > mm/filemap.c | 82 +++++++++++++++++++++++++++++++++++++---- > 2 files changed, 84 insertions(+), 7 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index d2147215d415..72101811524c 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -248,6 +248,15 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping, > #define FGP_NOFS 0x00000010 > #define FGP_NOWAIT 0x00000020 > #define FGP_FOR_MMAP 0x00000040 > +/* > + * If you add more flags, increment FGP_ORDER_SHIFT (no further than 25). Maybe some BUILD_BUG_ON()s to ensure FGP_ORDER_SHIFT is sane? > + * Do not insert flags above the FGP order bits. > + */ > +#define FGP_ORDER_SHIFT 7 > +#define FGP_PMD ((PMD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > +#define FGP_PUD ((PUD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > + > +#define fgp_order(fgp) ((fgp) >> FGP_ORDER_SHIFT) > > struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > int fgp_flags, gfp_t cache_gfp_mask); > diff --git a/mm/filemap.c b/mm/filemap.c > index ae3c0a70a8e9..904dfabbea52 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1572,7 +1572,71 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset) > > return page; > } > -EXPORT_SYMBOL(find_get_entry); > + > +static bool pagecache_is_conflict(struct page *page) > +{ > + return page == XA_RETRY_ENTRY; > +} > + > +/** > + * __find_get_page - Find and get a page cache entry. > + * @mapping: The address_space to search. > + * @offset: The page cache index. > + * @order: The minimum order of the entry to return. > + * > + * Looks up the page cache entries at @mapping between @offset and > + * @offset + 2^@order. If there is a page cache page, it is returned with Off by one? :P > + * an increased refcount unless it is smaller than @order. > + * > + * If the slot holds a shadow entry of a previously evicted page, or a > + * swap entry from shmem/tmpfs, it is returned. > + * > + * Return: the found page, a value indicating a conflicting page or %NULL if > + * there are no pages in this range. > + */ > +static struct page *__find_get_page(struct address_space *mapping, > + unsigned long offset, unsigned int order) > +{ > + XA_STATE(xas, &mapping->i_pages, offset); > + struct page *page; > + > + rcu_read_lock(); > +repeat: > + xas_reset(&xas); > + page = xas_find(&xas, offset | ((1UL << order) - 1)); Hm. '|' is confusing. What is expectation about offset? Is round_down(offset, 1UL << order) expected to be equal offset? If yes, please use '+' instead of '|'. > + if (xas_retry(&xas, page)) > + goto repeat; > + /* > + * A shadow entry of a recently evicted page, or a swap entry from > + * shmem/tmpfs. Skip it; keep looking for pages. > + */ > + if (xa_is_value(page)) > + goto repeat; > + if (!page) > + goto out; > + if (compound_order(page) < order) { > + page = XA_RETRY_ENTRY; > + goto out; > + } compound_order() is not stable if you don't have pin on the page. Check it after page_cache_get_speculative(). > + > + if (!page_cache_get_speculative(page)) > + goto repeat; > + > + /* > + * Has the page moved or been split? > + * This is part of the lockless pagecache protocol. See > + * include/linux/pagemap.h for details. > + */ > + if (unlikely(page != xas_reload(&xas))) { > + put_page(page); > + goto repeat; > + } > + page = find_subpage(page, offset); > +out: > + rcu_read_unlock(); > + > + return page; > +} > > /** > * find_lock_entry - locate, pin and lock a page cache entry > @@ -1614,12 +1678,12 @@ EXPORT_SYMBOL(find_lock_entry); > * pagecache_get_page - find and get a page reference > * @mapping: the address_space to search > * @offset: the page index > - * @fgp_flags: PCG flags > + * @fgp_flags: FGP flags > * @gfp_mask: gfp mask to use for the page cache data page allocation > * > * Looks up the page cache slot at @mapping & @offset. > * > - * PCG flags modify how the page is returned. > + * FGP flags modify how the page is returned. > * > * @fgp_flags can be: > * > @@ -1632,6 +1696,10 @@ EXPORT_SYMBOL(find_lock_entry); > * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do > * its own locking dance if the page is already in cache, or unlock the page > * before returning if we had to add the page to pagecache. > + * - FGP_PMD: We're only interested in pages at PMD granularity. If there > + * is no page here (and FGP_CREATE is set), we'll create one large enough. > + * If there is a smaller page in the cache that overlaps the PMD page, we > + * return %NULL and do not attempt to create a page. Is it really the best inteface? Maybe allow user to ask bitmask of allowed orders? For THP order-0 is fine if order-9 has failed. > * > * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even > * if the GFP flags specified for FGP_CREAT are atomic. > @@ -1646,9 +1714,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > struct page *page; > > repeat: > - page = find_get_entry(mapping, offset); > - if (xa_is_value(page)) > - page = NULL; > + page = __find_get_page(mapping, offset, fgp_order(fgp_flags)); > + if (pagecache_is_conflict(page)) > + return NULL; > if (!page) > goto no_page; > > @@ -1682,7 +1750,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > if (fgp_flags & FGP_NOFS) > gfp_mask &= ~__GFP_FS; > > - page = __page_cache_alloc(gfp_mask); > + page = __page_cache_alloc_order(gfp_mask, fgp_order(fgp_flags)); > if (!page) > return NULL; > > -- > 2.23.0.rc1 >
On Fri, Sep 06, 2019 at 03:59:28PM +0300, Kirill A. Shutemov wrote: > > @@ -248,6 +248,15 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping, > > #define FGP_NOFS 0x00000010 > > #define FGP_NOWAIT 0x00000020 > > #define FGP_FOR_MMAP 0x00000040 > > +/* > > + * If you add more flags, increment FGP_ORDER_SHIFT (no further than 25). > > Maybe some BUILD_BUG_ON()s to ensure FGP_ORDER_SHIFT is sane? Yeah, probably a good idea. > > +/** > > + * __find_get_page - Find and get a page cache entry. > > + * @mapping: The address_space to search. > > + * @offset: The page cache index. > > + * @order: The minimum order of the entry to return. > > + * > > + * Looks up the page cache entries at @mapping between @offset and > > + * @offset + 2^@order. If there is a page cache page, it is returned with > > Off by one? :P Hah! I thought it reasonable to be ambiguous in the English description ... it's not entirely uncommon to describe something being 'between A and B' when meaning ">= A and < B". > > +static struct page *__find_get_page(struct address_space *mapping, > > + unsigned long offset, unsigned int order) > > +{ > > + XA_STATE(xas, &mapping->i_pages, offset); > > + struct page *page; > > + > > + rcu_read_lock(); > > +repeat: > > + xas_reset(&xas); > > + page = xas_find(&xas, offset | ((1UL << order) - 1)); > > Hm. '|' is confusing. What is expectation about offset? > Is round_down(offset, 1UL << order) expected to be equal offset? > If yes, please use '+' instead of '|'. Might make sense to put in ... VM_BUG_ON(offset & ((1UL << order) - 1)); > > + if (xas_retry(&xas, page)) > > + goto repeat; > > + /* > > + * A shadow entry of a recently evicted page, or a swap entry from > > + * shmem/tmpfs. Skip it; keep looking for pages. > > + */ > > + if (xa_is_value(page)) > > + goto repeat; > > + if (!page) > > + goto out; > > + if (compound_order(page) < order) { > > + page = XA_RETRY_ENTRY; > > + goto out; > > + } > > compound_order() is not stable if you don't have pin on the page. > Check it after page_cache_get_speculative(). Maybe check both before and after? If we check it before, we don't bother to bump the refcount on a page which is too small. > > @@ -1632,6 +1696,10 @@ EXPORT_SYMBOL(find_lock_entry); > > * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do > > * its own locking dance if the page is already in cache, or unlock the page > > * before returning if we had to add the page to pagecache. > > + * - FGP_PMD: We're only interested in pages at PMD granularity. If there > > + * is no page here (and FGP_CREATE is set), we'll create one large enough. > > + * If there is a smaller page in the cache that overlaps the PMD page, we > > + * return %NULL and do not attempt to create a page. > > Is it really the best inteface? > > Maybe allow user to ask bitmask of allowed orders? For THP order-0 is fine > if order-9 has failed. That's the semantics that filemap_huge_fault() wants. If the page isn't available at order-9, it needs to return VM_FAULT_FALLBACK (and the VM will call into filemap_fault() to handle the regular sized fault). Now, maybe there are other users who want to specify "create a page of this size if you can, but if there's already something there smaller, return that". We can add another FGP flag when those show up ;-) Thanks for the review.
On Fri, Sep 06, 2019 at 06:41:45AM -0700, Matthew Wilcox wrote: > On Fri, Sep 06, 2019 at 03:59:28PM +0300, Kirill A. Shutemov wrote: > > > +/** > > > + * __find_get_page - Find and get a page cache entry. > > > + * @mapping: The address_space to search. > > > + * @offset: The page cache index. > > > + * @order: The minimum order of the entry to return. > > > + * > > > + * Looks up the page cache entries at @mapping between @offset and > > > + * @offset + 2^@order. If there is a page cache page, it is returned with > > > > Off by one? :P > > Hah! I thought it reasonable to be ambiguous in the English description > ... it's not entirely uncommon to describe something being 'between A > and B' when meaning ">= A and < B". It is reasable. I was just a nitpick. > > > + if (compound_order(page) < order) { > > > + page = XA_RETRY_ENTRY; > > > + goto out; > > > + } > > > > compound_order() is not stable if you don't have pin on the page. > > Check it after page_cache_get_speculative(). > > Maybe check both before and after? If we check it before, we don't bother > to bump the refcount on a page which is too small. Makes sense. False-positives should be rare enough to ignore them. > > > @@ -1632,6 +1696,10 @@ EXPORT_SYMBOL(find_lock_entry); > > > * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do > > > * its own locking dance if the page is already in cache, or unlock the page > > > * before returning if we had to add the page to pagecache. > > > + * - FGP_PMD: We're only interested in pages at PMD granularity. If there > > > + * is no page here (and FGP_CREATE is set), we'll create one large enough. > > > + * If there is a smaller page in the cache that overlaps the PMD page, we > > > + * return %NULL and do not attempt to create a page. > > > > Is it really the best inteface? > > > > Maybe allow user to ask bitmask of allowed orders? For THP order-0 is fine > > if order-9 has failed. > > That's the semantics that filemap_huge_fault() wants. If the page isn't > available at order-9, it needs to return VM_FAULT_FALLBACK (and the VM > will call into filemap_fault() to handle the regular sized fault). Ideally, we should not have division between ->fault and ->huge_fault. Integrating them together will give a shorter fallback loop and more flexible inteface here would give benefit. But I guess it's out-of-scope of the patchset.
On Fri, Sep 06, 2019 at 04:52:15PM +0300, Kirill A. Shutemov wrote: > On Fri, Sep 06, 2019 at 06:41:45AM -0700, Matthew Wilcox wrote: > > On Fri, Sep 06, 2019 at 03:59:28PM +0300, Kirill A. Shutemov wrote: > > > > + * - FGP_PMD: We're only interested in pages at PMD granularity. If there > > > > + * is no page here (and FGP_CREATE is set), we'll create one large enough. > > > > + * If there is a smaller page in the cache that overlaps the PMD page, we > > > > + * return %NULL and do not attempt to create a page. > > > > > > Is it really the best inteface? > > > > > > Maybe allow user to ask bitmask of allowed orders? For THP order-0 is fine > > > if order-9 has failed. > > > > That's the semantics that filemap_huge_fault() wants. If the page isn't > > available at order-9, it needs to return VM_FAULT_FALLBACK (and the VM > > will call into filemap_fault() to handle the regular sized fault). > > Ideally, we should not have division between ->fault and ->huge_fault. > Integrating them together will give a shorter fallback loop and more > flexible inteface here would give benefit. > > But I guess it's out-of-scope of the patchset. Heh, just a little bit ... there are about 150 occurrences of vm_operations_struct in the kernel, and I don't fancy one bit converting them all to use ->huge_fault instead of ->fault!
On 9/6/19 6:12 AM, Matthew Wilcox wrote: > On Fri, Sep 06, 2019 at 06:04:05AM +0800, kbuild test robot wrote: >> Hi Matthew, >> >> Thank you for the patch! Yet something to improve: >> >> [auto build test ERROR on linus/master] >> [cannot apply to v5.3-rc7 next-20190904] >> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] > It looks like you're not applying these to the -mm tree? I thought that > was included in -next. Hi, Sorry for the inconvenience, we'll look into it. and 0day-CI introduced '--base' option to record base tree info in format-patch. could you kindly add it to help robot to base on the right tree? please see https://stackoverflow.com/a/37406982 Best Regards, Rong Chen > > > _______________________________________________ > kbuild-all mailing list > kbuild-all@lists.01.org > https://lists.01.org/mailman/listinfo/kbuild-all
On Mon, Sep 09, 2019 at 08:42:03AM +0800, Rong Chen wrote: > > > On 9/6/19 6:12 AM, Matthew Wilcox wrote: > > On Fri, Sep 06, 2019 at 06:04:05AM +0800, kbuild test robot wrote: > > > Hi Matthew, > > > > > > Thank you for the patch! Yet something to improve: > > > > > > [auto build test ERROR on linus/master] > > > [cannot apply to v5.3-rc7 next-20190904] > > > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] > > It looks like you're not applying these to the -mm tree? I thought that > > was included in -next. > > Hi, > > Sorry for the inconvenience, we'll look into it. and 0day-CI introduced > '--base' option to record base tree info in format-patch. > could you kindly add it to help robot to base on the right tree? please see > https://stackoverflow.com/a/37406982 There isn't a stable git base tree to work from with mmotm: https://www.ozlabs.org/~akpm/mmotm/mmotm-readme.txt
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index d2147215d415..72101811524c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -248,6 +248,15 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping, #define FGP_NOFS 0x00000010 #define FGP_NOWAIT 0x00000020 #define FGP_FOR_MMAP 0x00000040 +/* + * If you add more flags, increment FGP_ORDER_SHIFT (no further than 25). + * Do not insert flags above the FGP order bits. + */ +#define FGP_ORDER_SHIFT 7 +#define FGP_PMD ((PMD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) +#define FGP_PUD ((PUD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) + +#define fgp_order(fgp) ((fgp) >> FGP_ORDER_SHIFT) struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, int fgp_flags, gfp_t cache_gfp_mask); diff --git a/mm/filemap.c b/mm/filemap.c index ae3c0a70a8e9..904dfabbea52 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1572,7 +1572,71 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset) return page; } -EXPORT_SYMBOL(find_get_entry); + +static bool pagecache_is_conflict(struct page *page) +{ + return page == XA_RETRY_ENTRY; +} + +/** + * __find_get_page - Find and get a page cache entry. + * @mapping: The address_space to search. + * @offset: The page cache index. + * @order: The minimum order of the entry to return. + * + * Looks up the page cache entries at @mapping between @offset and + * @offset + 2^@order. If there is a page cache page, it is returned with + * an increased refcount unless it is smaller than @order. + * + * If the slot holds a shadow entry of a previously evicted page, or a + * swap entry from shmem/tmpfs, it is returned. + * + * Return: the found page, a value indicating a conflicting page or %NULL if + * there are no pages in this range. + */ +static struct page *__find_get_page(struct address_space *mapping, + unsigned long offset, unsigned int order) +{ + XA_STATE(xas, &mapping->i_pages, offset); + struct page *page; + + rcu_read_lock(); +repeat: + xas_reset(&xas); + page = xas_find(&xas, offset | ((1UL << order) - 1)); + if (xas_retry(&xas, page)) + goto repeat; + /* + * A shadow entry of a recently evicted page, or a swap entry from + * shmem/tmpfs. Skip it; keep looking for pages. + */ + if (xa_is_value(page)) + goto repeat; + if (!page) + goto out; + if (compound_order(page) < order) { + page = XA_RETRY_ENTRY; + goto out; + } + + if (!page_cache_get_speculative(page)) + goto repeat; + + /* + * Has the page moved or been split? + * This is part of the lockless pagecache protocol. See + * include/linux/pagemap.h for details. + */ + if (unlikely(page != xas_reload(&xas))) { + put_page(page); + goto repeat; + } + page = find_subpage(page, offset); +out: + rcu_read_unlock(); + + return page; +} /** * find_lock_entry - locate, pin and lock a page cache entry @@ -1614,12 +1678,12 @@ EXPORT_SYMBOL(find_lock_entry); * pagecache_get_page - find and get a page reference * @mapping: the address_space to search * @offset: the page index - * @fgp_flags: PCG flags + * @fgp_flags: FGP flags * @gfp_mask: gfp mask to use for the page cache data page allocation * * Looks up the page cache slot at @mapping & @offset. * - * PCG flags modify how the page is returned. + * FGP flags modify how the page is returned. * * @fgp_flags can be: * @@ -1632,6 +1696,10 @@ EXPORT_SYMBOL(find_lock_entry); * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do * its own locking dance if the page is already in cache, or unlock the page * before returning if we had to add the page to pagecache. + * - FGP_PMD: We're only interested in pages at PMD granularity. If there + * is no page here (and FGP_CREATE is set), we'll create one large enough. + * If there is a smaller page in the cache that overlaps the PMD page, we + * return %NULL and do not attempt to create a page. * * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even * if the GFP flags specified for FGP_CREAT are atomic. @@ -1646,9 +1714,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, struct page *page; repeat: - page = find_get_entry(mapping, offset); - if (xa_is_value(page)) - page = NULL; + page = __find_get_page(mapping, offset, fgp_order(fgp_flags)); + if (pagecache_is_conflict(page)) + return NULL; if (!page) goto no_page; @@ -1682,7 +1750,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, if (fgp_flags & FGP_NOFS) gfp_mask &= ~__GFP_FS; - page = __page_cache_alloc(gfp_mask); + page = __page_cache_alloc_order(gfp_mask, fgp_order(fgp_flags)); if (!page) return NULL;