Hi Sam Am 10.02.22 um 22:00 schrieb Sam Ravnborg:
Hi Thomas, On Thu, Feb 10, 2022 at 03:11:11PM +0100, Thomas Zimmermann wrote:Return early if a page is already in the list of dirty pages for deferred I/O. This can be detected if the page's list head is not empty. Keep the list head initialized while the page is not enlisted to make this work reliably. Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx> --- drivers/video/fbdev/core/fb_defio.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index a591d291b231..3727b1ca87b1 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -59,6 +59,7 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) printk(KERN_ERR "no mapping available\n");BUG_ON(!page->mapping);+ INIT_LIST_HEAD(&page->lru); page->index = vmf->pgoff;vmf->page = page;@@ -122,17 +123,19 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) */ lock_page(page);+ /*+ * This check is to catch the case where a new process could start + * writing to the same page through a new pte. this new access + * can cause the mkwrite even when the original ps's pte is marked + * writable. + */When moving this comment it would be prudent to also fix the wording a bit. - Capital in start of sentence and after a period - Spell out process and do not shorten ps
Ok.
+ if (!list_empty(&page->lru)) + goto page_already_added; +This check says that if the page already has something in the parge->lru then this is added by defio and thus is already added. This matches your commit description - OK. Maybe add something like: * Pages added will have their lru set, and it is clered again in the * deferred work handler.
I'll add a related TODO to the comment because we actually want to remove the use of the lru field. It's owned by the page cache. I already have a prototype patch that implements the page tracking with a separate list.
Best regards Thomas
/* we loop through the pagelist before adding in order to keep the pagelist sorted */ list_for_each_entry(cur, &fbdefio->pagelist, lru) { - /* this check is to catch the case where a new - process could start writing to the same page - through a new pte. this new access can cause the - mkwrite even when the original ps's pte is marked - writable */ - if (unlikely(cur == page)) - goto page_already_added; - else if (cur->index > page->index) + if (cur->index > page->index) break; }@@ -194,7 +197,7 @@ static void fb_deferred_io_work(struct work_struct *work) /* clear the list */list_for_each_safe(node, next, &fbdefio->pagelist) { - list_del(node); + list_del_init(node); } mutex_unlock(&fbdefio->lock); }With the comment adjusted as you see fit Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
