| Message ID | 20240903083818.3071759-2-link@vivo.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | udmbuf bug fix and some improvements | expand |
Hi Huan, > Subject: [PATCH v5 1/7] udmabuf: pre-fault when first page fault > > The current udmabuf mmap uses a page fault to populate the vma. > > However, the current udmabuf has already obtained and pinned the folio > upon completion of the creation.This means that the physical memory has > already been acquired, rather than being accessed dynamically. > > As a result, the page fault has lost its purpose as a demanding > page. Due to the fact that page fault requires trapping into kernel mode > and filling in when accessing the corresponding virtual address in mmap, > when creating a large size udmabuf, this represents a considerable > overhead. > > This patch first the pfn into page table, and then pre-fault each pfn > into vma, when first access. Should know, if anything wrong when > pre-fault, will not report it's error, else, report when task access it > at the first time. > > Suggested-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > Signed-off-by: Huan Yang <link@vivo.com> > --- > drivers/dma-buf/udmabuf.c | 35 +++++++++++++++++++++++++++++++++-- > 1 file changed, 33 insertions(+), 2 deletions(-) > > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c > index 047c3cd2ceff..0a8c231a36e1 100644 > --- a/drivers/dma-buf/udmabuf.c > +++ b/drivers/dma-buf/udmabuf.c > @@ -43,7 +43,8 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault > *vmf) > struct vm_area_struct *vma = vmf->vma; > struct udmabuf *ubuf = vma->vm_private_data; > pgoff_t pgoff = vmf->pgoff; > - unsigned long pfn; > + unsigned long addr, end, pfn; > + vm_fault_t ret; > > if (pgoff >= ubuf->pagecount) > return VM_FAULT_SIGBUS; > @@ -51,7 +52,37 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault > *vmf) > pfn = folio_pfn(ubuf->folios[pgoff]); > pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; > > - return vmf_insert_pfn(vma, vmf->address, pfn); > + ret = vmf_insert_pfn(vma, vmf->address, pfn); > + if (ret & VM_FAULT_ERROR) > + return ret; > + > + /* pre fault */ > + pgoff = vma->vm_pgoff; > + end = vma->vm_end; Nit: use vma->vm_end directly in the loop below, as end is used only once. > + addr = vma->vm_start; > + > + for (; addr < end; pgoff++, addr += PAGE_SIZE) { > + if (addr == vmf->address) > + continue; > + > + if (WARN_ON(pgoff >= ubuf->pagecount)) > + break; > + > + pfn = folio_pfn(ubuf->folios[pgoff]); > + Nit: no need for a blank line here. > + pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; > + > + /** > + * If something wrong, due to this vm fault success, > + * do not report in here, report only when true access > + * this addr. > + * So, don't update ret here, just break. Please rewrite the above comments as: * If the below vmf_insert_pfn() fails, we do not return an error here * during this pre-fault step. However, an error will be returned if the * failure occurs when the addr is truly accessed. With that, Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > + */ > + if (vmf_insert_pfn(vma, addr, pfn) & VM_FAULT_ERROR) > + break; > + } > + > + return ret; > } > > static const struct vm_operations_struct udmabuf_vm_ops = { > -- > 2.45.2
在 2024/9/6 16:12, Kasireddy, Vivek 写道: > Hi Huan, > >> Subject: [PATCH v5 1/7] udmabuf: pre-fault when first page fault >> >> The current udmabuf mmap uses a page fault to populate the vma. >> >> However, the current udmabuf has already obtained and pinned the folio >> upon completion of the creation.This means that the physical memory has >> already been acquired, rather than being accessed dynamically. >> >> As a result, the page fault has lost its purpose as a demanding >> page. Due to the fact that page fault requires trapping into kernel mode >> and filling in when accessing the corresponding virtual address in mmap, >> when creating a large size udmabuf, this represents a considerable >> overhead. >> >> This patch first the pfn into page table, and then pre-fault each pfn >> into vma, when first access. Should know, if anything wrong when >> pre-fault, will not report it's error, else, report when task access it >> at the first time. >> >> Suggested-by: Vivek Kasireddy <vivek.kasireddy@intel.com> >> Signed-off-by: Huan Yang <link@vivo.com> >> --- >> drivers/dma-buf/udmabuf.c | 35 +++++++++++++++++++++++++++++++++-- >> 1 file changed, 33 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c >> index 047c3cd2ceff..0a8c231a36e1 100644 >> --- a/drivers/dma-buf/udmabuf.c >> +++ b/drivers/dma-buf/udmabuf.c >> @@ -43,7 +43,8 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault >> *vmf) >> struct vm_area_struct *vma = vmf->vma; >> struct udmabuf *ubuf = vma->vm_private_data; >> pgoff_t pgoff = vmf->pgoff; >> - unsigned long pfn; >> + unsigned long addr, end, pfn; >> + vm_fault_t ret; >> >> if (pgoff >= ubuf->pagecount) >> return VM_FAULT_SIGBUS; >> @@ -51,7 +52,37 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault >> *vmf) >> pfn = folio_pfn(ubuf->folios[pgoff]); >> pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; >> >> - return vmf_insert_pfn(vma, vmf->address, pfn); >> + ret = vmf_insert_pfn(vma, vmf->address, pfn); >> + if (ret & VM_FAULT_ERROR) >> + return ret; >> + >> + /* pre fault */ >> + pgoff = vma->vm_pgoff; >> + end = vma->vm_end; > Nit: use vma->vm_end directly in the loop below, as end is used only once. > >> + addr = vma->vm_start; >> + >> + for (; addr < end; pgoff++, addr += PAGE_SIZE) { >> + if (addr == vmf->address) >> + continue; >> + >> + if (WARN_ON(pgoff >= ubuf->pagecount)) >> + break; >> + >> + pfn = folio_pfn(ubuf->folios[pgoff]); >> + > Nit: no need for a blank line here. > >> + pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; >> + >> + /** >> + * If something wrong, due to this vm fault success, >> + * do not report in here, report only when true access >> + * this addr. >> + * So, don't update ret here, just break. > Please rewrite the above comments as: > * If the below vmf_insert_pfn() fails, we do not return an error here > * during this pre-fault step. However, an error will be returned if the > * failure occurs when the addr is truly accessed. Thank you > > With that, OK. Thanks > Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > >> + */ >> + if (vmf_insert_pfn(vma, addr, pfn) & VM_FAULT_ERROR) >> + break; >> + } >> + >> + return ret; >> } >> >> static const struct vm_operations_struct udmabuf_vm_ops = { >> -- >> 2.45.2
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 047c3cd2ceff..0a8c231a36e1 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -43,7 +43,8 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf) struct vm_area_struct *vma = vmf->vma; struct udmabuf *ubuf = vma->vm_private_data; pgoff_t pgoff = vmf->pgoff; - unsigned long pfn; + unsigned long addr, end, pfn; + vm_fault_t ret; if (pgoff >= ubuf->pagecount) return VM_FAULT_SIGBUS; @@ -51,7 +52,37 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf) pfn = folio_pfn(ubuf->folios[pgoff]); pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; - return vmf_insert_pfn(vma, vmf->address, pfn); + ret = vmf_insert_pfn(vma, vmf->address, pfn); + if (ret & VM_FAULT_ERROR) + return ret; + + /* pre fault */ + pgoff = vma->vm_pgoff; + end = vma->vm_end; + addr = vma->vm_start; + + for (; addr < end; pgoff++, addr += PAGE_SIZE) { + if (addr == vmf->address) + continue; + + if (WARN_ON(pgoff >= ubuf->pagecount)) + break; + + pfn = folio_pfn(ubuf->folios[pgoff]); + + pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT; + + /** + * If something wrong, due to this vm fault success, + * do not report in here, report only when true access + * this addr. + * So, don't update ret here, just break. + */ + if (vmf_insert_pfn(vma, addr, pfn) & VM_FAULT_ERROR) + break; + } + + return ret; } static const struct vm_operations_struct udmabuf_vm_ops = {
The current udmabuf mmap uses a page fault to populate the vma. However, the current udmabuf has already obtained and pinned the folio upon completion of the creation.This means that the physical memory has already been acquired, rather than being accessed dynamically. As a result, the page fault has lost its purpose as a demanding page. Due to the fact that page fault requires trapping into kernel mode and filling in when accessing the corresponding virtual address in mmap, when creating a large size udmabuf, this represents a considerable overhead. This patch first the pfn into page table, and then pre-fault each pfn into vma, when first access. Should know, if anything wrong when pre-fault, will not report it's error, else, report when task access it at the first time. Suggested-by: Vivek Kasireddy <vivek.kasireddy@intel.com> Signed-off-by: Huan Yang <link@vivo.com> --- drivers/dma-buf/udmabuf.c | 35 +++++++++++++++++++++++++++++++++-- 1 file changed, 33 insertions(+), 2 deletions(-)