From: Souptick Joarder <jrdr.linux@xxxxxxxxx> Subject: mm/gup.c: update the documentation This patch is an attempt to update the documentation. * Add/ remove extra * based on type of function static/global. * Add description for functions and their input arguments. [akpm@xxxxxxxxxxxxxxxxxxxx: s@/*@/**@] Link: http://lkml.kernel.org/r/1588013630-4497-1-git-send-email-jrdr.linux@xxxxxxxxx Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 57 ++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 39 insertions(+), 18 deletions(-) --- a/mm/gup.c~mm-gupc-updating-the-documentation +++ a/mm/gup.c @@ -1168,7 +1168,7 @@ static bool vma_permits_fault(struct vm_ return true; } -/* +/** * fixup_user_fault() - manually resolve a user page fault * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded. @@ -1839,7 +1839,7 @@ static long __get_user_pages_remote(stru gup_flags | FOLL_TOUCH | FOLL_REMOTE); } -/* +/** * get_user_pages_remote() - pin user pages in memory * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded. @@ -1870,13 +1870,13 @@ static long __get_user_pages_remote(stru * * Must be called with mmap_sem held for read or write. * - * get_user_pages walks a process's page tables and takes a reference to - * each struct page that each user address corresponds to at a given + * get_user_pages_remote walks a process's page tables and takes a reference + * to each struct page that each user address corresponds to at a given * instant. That is, it takes the page that would be accessed if a user * thread accesses the given user virtual address at that instant. * * This does not guarantee that the page exists in the user mappings when - * get_user_pages returns, and there may even be a completely different + * get_user_pages_remote returns, and there may even be a completely different * page there in some cases (eg. if mmapped pagecache has been invalidated * and subsequently re faulted). However it does guarantee that the page * won't be freed completely. And mostly callers simply care that the page @@ -1888,17 +1888,17 @@ static long __get_user_pages_remote(stru * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must * be called after the page is finished with, and before put_page is called. * - * get_user_pages is typically used for fewer-copy IO operations, to get a - * handle on the memory by some means other than accesses via the user virtual - * addresses. The pages may be submitted for DMA to devices or accessed via - * their kernel linear mapping (via the kmap APIs). Care should be taken to - * use the correct cache flushing APIs. + * get_user_pages_remote is typically used for fewer-copy IO operations, + * to get a handle on the memory by some means other than accesses + * via the user virtual addresses. The pages may be submitted for + * DMA to devices or accessed via their kernel linear mapping (via the + * kmap APIs). Care should be taken to use the correct cache flushing APIs. * * See also get_user_pages_fast, for performance critical applications. * - * get_user_pages should be phased out in favor of + * get_user_pages_remote should be phased out in favor of * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing - * should use get_user_pages because it cannot pass + * should use get_user_pages_remote because it cannot pass * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault. */ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, @@ -1937,7 +1937,17 @@ static long __get_user_pages_remote(stru } #endif /* !CONFIG_MMU */ -/* +/** + * get_user_pages() - pin user pages in memory + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying lookup behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. Or NULL, if caller + * only intends to ensure the pages are faulted in. + * @vmas: array of pointers to vmas corresponding to each page. + * Or NULL if the caller does not require them. + * * This is the same as get_user_pages_remote(), just with a * less-flexible calling convention where we assume that the task * and mm being operated on are the current task's and don't allow @@ -1960,11 +1970,7 @@ long get_user_pages(unsigned long start, } EXPORT_SYMBOL(get_user_pages); -/* - * We can leverage the VM_FAULT_RETRY functionality in the page fault - * paths better by using either get_user_pages_locked() or - * get_user_pages_unlocked(). - * +/** * get_user_pages_locked() is suitable to replace the form: * * down_read(&mm->mmap_sem); @@ -1980,6 +1986,21 @@ EXPORT_SYMBOL(get_user_pages); * get_user_pages_locked(tsk, mm, ..., pages, &locked); * if (locked) * up_read(&mm->mmap_sem); + * + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying lookup behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. Or NULL, if caller + * only intends to ensure the pages are faulted in. + * @locked: pointer to lock flag indicating whether lock is held and + * subsequently whether VM_FAULT_RETRY functionality can be + * utilised. Lock must initially be held. + * + * We can leverage the VM_FAULT_RETRY functionality in the page fault + * paths better by using either get_user_pages_locked() or + * get_user_pages_unlocked(). + * */ long get_user_pages_locked(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, _
