linux-kernel - Re: [PATCH 1/3] mm: add apply_to_existing

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Message-Id: <20191206163853.cdeb5dc80a8622fb6323a8d2@linux-foundation.org>
Date:   Fri, 6 Dec 2019 16:38:53 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Daniel Axtens <dja@...ens.net>
Cc:     kasan-dev@...glegroups.com, linux-mm@...ck.org,
        aryabinin@...tuozzo.com, glider@...gle.com,
        linux-kernel@...r.kernel.org, dvyukov@...gle.com,
        daniel@...earbox.net, cai@....pw
Subject: Re: [PATCH 1/3] mm: add apply_to_existing_pages helper

On Fri,  6 Dec 2019 01:04:05 +1100 Daniel Axtens <dja@...ens.net> wrote:

> apply_to_page_range takes an address range, and if any parts of it
> are not covered by the existing page table hierarchy, it allocates
> memory to fill them in.
> 
> In some use cases, this is not what we want - we want to be able to
> operate exclusively on PTEs that are already in the tables.
> 
> Add apply_to_existing_pages for this. Adjust the walker functions
> for apply_to_page_range to take 'create', which switches them between
> the old and new modes.

Wouldn't apply_to_existing_page_range() be a better name?

--- a/include/linux/mm.h~mm-add-apply_to_existing_pages-helper-fix-fix
+++ a/include/linux/mm.h
@@ -2621,9 +2621,9 @@ static inline int vm_fault_to_errno(vm_f
 typedef int (*pte_fn_t)(pte_t *pte, unsigned long addr, void *data);
 extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 			       unsigned long size, pte_fn_t fn, void *data);
-extern int apply_to_existing_pages(struct mm_struct *mm, unsigned long address,
-				   unsigned long size, pte_fn_t fn,
-				   void *data);
+extern int apply_to_existing_page_range(struct mm_struct *mm,
+				   unsigned long address, unsigned long size,
+				   pte_fn_t fn, void *data);
 
 #ifdef CONFIG_PAGE_POISONING
 extern bool page_poisoning_enabled(void);
--- a/mm/memory.c~mm-add-apply_to_existing_pages-helper-fix-fix
+++ a/mm/memory.c
@@ -2184,12 +2184,12 @@ EXPORT_SYMBOL_GPL(apply_to_page_range);
  * Unlike apply_to_page_range, this does _not_ fill in page tables
  * where they are absent.
  */
-int apply_to_existing_pages(struct mm_struct *mm, unsigned long addr,
-			    unsigned long size, pte_fn_t fn, void *data)
+int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
+				 unsigned long size, pte_fn_t fn, void *data)
 {
 	return __apply_to_page_range(mm, addr, size, fn, data, false);
 }
-EXPORT_SYMBOL_GPL(apply_to_existing_pages);
+EXPORT_SYMBOL_GPL(apply_to_existing_page_range);
 
 /*
  * handle_pte_fault chooses page fault handler according to an entry which was
_