improve read ahead in kernel

Subject: [PATCH] when system in low memory scenario, imaging there is a mp3
play, or video play, we need to read mp3 or video file
from memory to page cache,but when system lack of memory,
page cache of mp3 or video file will be reclaimed.once read
in memory, then reclaimed, it will cause audio or video glitch,and it will increase the io operation at the same
time.

Signed-off-by xiaobing tu <[email protected]>

---
 include/linux/mm_types.h |    4 ++++
 mm/Kconfig               |    6 ++++++
 mm/filemap.c             |    4 ++++
 mm/readahead.c           |   20 +++++++++++++++++---
 mm/vmscan.c              |   10 ++++++++--
 5 files changed, 39 insertions(+), 5 deletions(-)

include/linux/mm_types.h +4 -0

index 5b42f1b..541864d 100644
@@ -149,6 +149,10 @@ struct page {
      */
     void *shadow;
 #endif
+#ifdef CONFIG_LOWMEMORY_READAHEAD
+    unsigned int ioprio;
+#endif
+
 }
 /*
  * If another subsystem starts using the double word pairing for atomic

mm/Kconfig +0 -0

index e338407..dade8d3 100644

mm/Kconfig +2 -0

+
+
 # eventually, we can have this option just 'select SPARSEMEM'
 config MEMORY_HOTPLUG
     bool "Allow for memory hot-add"

mm/filemap.c +4 -0

index a0701e6..e32efed8 100644
@@ -129,6 +129,10 @@ void __delete_from_page_cache(struct page *page)
     page->mapping = NULL;
     /* Leave page->index set: truncation lookup relies upon it */
     mapping->nrpages--;
+    #ifdef CONFIG_LOWMEMORY_READAHEAD
+    page->ioprio = 0;
+    #endif
+
     __dec_zone_page_state(page, NR_FILE_PAGES);
     if (PageSwapBacked(page))
         __dec_zone_page_state(page, NR_SHMEM);

mm/readahead.c +17 -3

index cbcbb02..dd07cfe 100644
@@ -159,6 +159,11 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
     int page_idx;
     int ret = 0;
     loff_t isize = i_size_read(inode);
+#ifdef CONFIG_LOWMEMORY_READAHEAD
+    int class = 0;
+    if (p->io_context)
+    class = IOPRIO_PRIO_CLASS(p->io_context->ioprio);
+#endif
 
     if (isize == 0)
         goto out;

@@ -177,12 +182,21 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
         rcu_read_lock();
         page = radix_tree_lookup(&mapping->page_tree, page_offset);
         rcu_read_unlock();
-        if (page)
-            continue;
-
+        if (page){
+#ifdef CONFIG_LOWMEMORY_READAHEAD
+            if (class == IOPRIO_CLASS_RT) {
+                page->ioprio = 1;
+#endif
+                continue;
+            }
         page = page_cache_alloc_readahead(mapping);
         if (!page)
             break;
+#ifdef CONFIG_LOWMEMORY_READAHEAD
+        if (class == IOPRIO_CLASS_RT) {
+            page->ioprio = 1;
+#endif
+
         page->index = page_offset;
         list_add(&page->lru, &page_pool);
         if (page_idx == nr_to_read - lookahead_size)

mm/vmscan.c +8 -2

index 753a2dc..86e03aa 100644
@@ -728,8 +728,14 @@ static enum page_references page_check_references(struct page *page,
     }
 
     /* Reclaim if clean, defer dirty pages to writeback */
-    if (referenced_page && !PageSwapBacked(page))
-        return PAGEREF_RECLAIM_CLEAN;
+    if (referenced_page && !PageSwapBacked(page)) {
+#ifdef CONFIG_LOWMEMORY_READAHEAD
+        if (page->ioprio == 1) {
+            return PAGEREF_ACTIVATE;
+        } else
+#endif
+            return PAGEREF_RECLAIM_CLEAN;
+    }
 
     return PAGEREF_RECLAIM;
 }

resend it, due to format error

Subject: [PATCH] when system in low memory scenario, imaging there is a mp3
play, ora video play, we need to read mp3 or video file
from memory to page cache,but when system lack of memory,
page cache of mp3 or video file will be reclaimed.once read
in memory, then reclaimed, it will cause audio or video glitch,and it will increase the io operation at the same
time.

Quoted 9 lines · xtu4 <[email protected]> wrote:

resend it, due to format error

Subject: [PATCH] when system in low memory scenario, imaging there is a mp3
play, ora video play, we need to read mp3 or video file
from memory to page cache,but when system lack of memory,
page cache of mp3 or video file will be reclaimed.once read
in memory, then reclaimed, it will cause audio or video glitch,and it will increase the io operation at the same
time.

To me, this basically describes how POSIX_FADV_NOREUSE should work.

I would like to have this ability via fadvise (and not CONFIG_).

Also, I think your patch has too many #ifdefs to be accepted.

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Quoted 11 lines

Quoted 9 lines · ?xtu4 <[email protected]> wrote:

?resend it, due to format error

?Subject: [PATCH] when system in low memory scenario, imaging there is a mp3 ??play, ora video play, we need to read mp3 or video file
??from memory to page cache,but when system lack of memory, ??page cache of mp3 or video file will be reclaimed.once read ??in memory, then reclaimed, it will cause audio or video ??glitch,and it will increase the io operation at the same ??time.

Quoted 1 line

?To me, this basically describes how POSIX_FADV_NOREUSE should work.

Hi Eric,

But why fadvise POSIX_FADV_NOREUSE almost do nothing? Why not set some flag or other things for these use once data?

Quoted 10 lines

?I would like to have this ability via fadvise (and not CONFIG_).

?Also, I think your patch has too many #ifdefs to be accepted.

?--
?To unsubscribe, send a message with 'unsubscribe linux-mm' in ?the body to [email protected]. ?For more info on Linux MM, ?see: http://www.linux-mm.org/ .
?Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

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