Hi, On Tue, Jan 30, 2024 at 10:50:00AM +0530, Anshuman Khandual wrote: > > > On 1/25/24 22:12, Alexandru Elisei wrote: > > Today, cma_alloc() is used to allocate a contiguous memory region. The > > function allows the caller to specify the number of pages to allocate, but > > not the starting address. cma_alloc() will walk over the entire CMA region > > trying to allocate the first available range of the specified size. > > > > Introduce cma_alloc_range(), which makes CMA more versatile by allowing the > > caller to specify a particular range in the CMA region, defined by the > > start pfn and the size. > > > > arm64 will make use of this function when tag storage management will be > > implemented: cma_alloc_range() will be used to reserve the tag storage > > associated with a tagged page. > > Basically, you would like to pass on a preferred start address and the > allocation could just fail if a contig range is not available from such > a starting address ? > > Then why not just change cma_alloc() to take a new argument 'start_pfn'. > Why create a new but almost similar allocator ? I tried doing that, and I gave up because: - It made cma_alloc() even more complex and hard to follow. - What value should 'start_pfn' be to tell cma_alloc() that it should be ignored? Or, to put it another way, what pfn number is invalid on **all** platforms that Linux supports? I can give it another go if we can come up with an invalid value for 'start_pfn'. > > But then I am wondering why this could not be done in the arm64 platform > code itself operating on a CMA area reserved just for tag storage. Unless > this new allocator has other usage beyond MTE, this could be implemented > in the platform itself. I had the same idea in the previous iteration, David Hildenbrand suggested this approach [1]. [1] https://lore.kernel.org/linux-fsdevel/2aafd53f-af1f-45f3-a08c-d11962254315@xxxxxxxxxx/ Thanks, Alex > > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> > > --- > > > > Changes since rfc v2: > > > > * New patch. > > > > include/linux/cma.h | 2 + > > include/trace/events/cma.h | 59 ++++++++++++++++++++++++++ > > mm/cma.c | 86 ++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 147 insertions(+) > > > > diff --git a/include/linux/cma.h b/include/linux/cma.h > > index 63873b93deaa..e32559da6942 100644 > > --- a/include/linux/cma.h > > +++ b/include/linux/cma.h > > @@ -50,6 +50,8 @@ extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size, > > struct cma **res_cma); > > extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align, > > bool no_warn); > > +extern int cma_alloc_range(struct cma *cma, unsigned long start, unsigned long count, > > + unsigned tries, gfp_t gfp); > > extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned long count); > > extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long count); > > > > diff --git a/include/trace/events/cma.h b/include/trace/events/cma.h > > index 25103e67737c..a89af313a572 100644 > > --- a/include/trace/events/cma.h > > +++ b/include/trace/events/cma.h > > @@ -36,6 +36,65 @@ TRACE_EVENT(cma_release, > > __entry->count) > > ); > > > > +TRACE_EVENT(cma_alloc_range_start, > > + > > + TP_PROTO(const char *name, unsigned long start, unsigned long count, > > + unsigned tries), > > + > > + TP_ARGS(name, start, count, tries), > > + > > + TP_STRUCT__entry( > > + __string(name, name) > > + __field(unsigned long, start) > > + __field(unsigned long, count) > > + __field(unsigned, tries) > > + ), > > + > > + TP_fast_assign( > > + __assign_str(name, name); > > + __entry->start = start; > > + __entry->count = count; > > + __entry->tries = tries; > > + ), > > + > > + TP_printk("name=%s start=%lx count=%lu tries=%u", > > + __get_str(name), > > + __entry->start, > > + __entry->count, > > + __entry->tries) > > +); > > + > > +TRACE_EVENT(cma_alloc_range_finish, > > + > > + TP_PROTO(const char *name, unsigned long start, unsigned long count, > > + unsigned attempts, int err), > > + > > + TP_ARGS(name, start, count, attempts, err), > > + > > + TP_STRUCT__entry( > > + __string(name, name) > > + __field(unsigned long, start) > > + __field(unsigned long, count) > > + __field(unsigned, attempts) > > + __field(int, err) > > + ), > > + > > + TP_fast_assign( > > + __assign_str(name, name); > > + __entry->start = start; > > + __entry->count = count; > > + __entry->attempts = attempts; > > + __entry->err = err; > > + ), > > + > > + TP_printk("name=%s start=%lx count=%lu attempts=%u err=%d", > > + __get_str(name), > > + __entry->start, > > + __entry->count, > > + __entry->attempts, > > + __entry->err) > > +); > > + > > TRACE_EVENT(cma_alloc_start, > > > > TP_PROTO(const char *name, unsigned long count, unsigned int align), > > diff --git a/mm/cma.c b/mm/cma.c > > index 543bb6b3be8e..4a0f68b9443b 100644 > > --- a/mm/cma.c > > +++ b/mm/cma.c > > @@ -416,6 +416,92 @@ static void cma_debug_show_areas(struct cma *cma) > > static inline void cma_debug_show_areas(struct cma *cma) { } > > #endif > > > > +/** > > + * cma_alloc_range() - allocate pages in a specific range > > + * @cma: Contiguous memory region for which the allocation is performed. > > + * @start: Starting pfn of the allocation. > > + * @count: Requested number of pages > > + * @tries: Number of tries if the range is busy > > + * @no_warn: Avoid printing message about failed allocation > > + * > > + * This function allocates part of contiguous memory from a specific contiguous > > + * memory area, from the specified starting address. The 'start' pfn and the the > > + * 'count' number of pages must be aligned to the CMA bitmap order per bit. > > + */ > > +int cma_alloc_range(struct cma *cma, unsigned long start, unsigned long count, > > + unsigned tries, gfp_t gfp) > > +{ > > + unsigned long bitmap_maxno, bitmap_no, bitmap_start, bitmap_count; > > + unsigned long i = 0; > > + struct page *page; > > + int err = -EINVAL; > > + > > + if (!cma || !cma->count || !cma->bitmap) > > + goto out_stats; > > + > > + trace_cma_alloc_range_start(cma->name, start, count, tries); > > + > > + if (!count || start < cma->base_pfn || > > + start + count > cma->base_pfn + cma->count) > > + goto out_stats; > > + > > + if (!IS_ALIGNED(start | count, 1 << cma->order_per_bit)) > > + goto out_stats; > > + > > + bitmap_start = (start - cma->base_pfn) >> cma->order_per_bit; > > + bitmap_maxno = cma_bitmap_maxno(cma); > > + bitmap_count = cma_bitmap_pages_to_bits(cma, count); > > + > > + spin_lock_irq(&cma->lock); > > + bitmap_no = bitmap_find_next_zero_area(cma->bitmap, bitmap_maxno, > > + bitmap_start, bitmap_count, 0); > > + if (bitmap_no != bitmap_start) { > > + spin_unlock_irq(&cma->lock); > > + err = -EEXIST; > > + goto out_stats; > > + } > > + bitmap_set(cma->bitmap, bitmap_start, bitmap_count); > > + spin_unlock_irq(&cma->lock); > > + > > + for (i = 0; i < tries; i++) { > > + mutex_lock(&cma_mutex); > > + err = alloc_contig_range(start, start + count, MIGRATE_CMA, gfp); > > + mutex_unlock(&cma_mutex); > > + > > + if (err != -EBUSY) > > + break; > > + } > > + > > + if (err) { > > + cma_clear_bitmap(cma, start, count); > > + } else { > > + page = pfn_to_page(start); > > + > > + /* > > + * CMA can allocate multiple page blocks, which results in > > + * different blocks being marked with different tags. Reset the > > + * tags to ignore those page blocks. > > + */ > > + for (i = 0; i < count; i++) > > + page_kasan_tag_reset(nth_page(page, i)); > > + } > > + > > +out_stats: > > + trace_cma_alloc_range_finish(cma->name, start, count, i, err); > > + > > + if (err) { > > + count_vm_events(CMA_ALLOC_FAIL, count); > > + if (cma) > > + cma_sysfs_account_fail_pages(cma, count); > > + } else { > > + count_vm_events(CMA_ALLOC_SUCCESS, count); > > + cma_sysfs_account_success_pages(cma, count); > > + } > > + > > + return err; > > +} > > + > > + > > /** > > * cma_alloc() - allocate pages from contiguous area > > * @cma: Contiguous memory region for which the allocation is performed. >
