The patch titled
Subject: readahead: drop dead code in ondemand_readahead()
has been added to the -mm mm-unstable branch. Its filename is
readahead-drop-dead-code-in-ondemand_readahead.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/readahead-drop-dead-code-in-ondemand_readahead.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: readahead: drop dead code in ondemand_readahead()
Date: Tue, 25 Jun 2024 12:18:57 +0200
ondemand_readahead() scales up the readahead window if the current read
would hit the readahead mark placed by itself. However the condition is
mostly dead code because:
a) In case of async readahead we always increase ra->start so ra->start
== index is never true.
b) In case of sync readahead we either go through
try_context_readahead() in which case ra->async_size == 1 < ra->size or
we go through initial_readahead where ra->async_size == ra->size iff
ra->size == max_pages.
So the only practical effect is reducing async_size for large initial
reads. Make the code more obvious.
Link: https://lkml.kernel.org/r/20240625101909.12234-7-jack@xxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 21 ++-------------------
1 file changed, 2 insertions(+), 19 deletions(-)
--- a/mm/readahead.c~readahead-drop-dead-code-in-ondemand_readahead
+++ a/mm/readahead.c
@@ -549,7 +549,6 @@ static void ondemand_readahead(struct re
struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
struct file_ra_state *ra = ractl->ra;
unsigned long max_pages = ra->ra_pages;
- unsigned long add_pages;
pgoff_t index = readahead_index(ractl);
pgoff_t expected, prev_index;
unsigned int order = folio ? folio_order(folio) : 0;
@@ -638,26 +637,10 @@ static void ondemand_readahead(struct re
initial_readahead:
ra->start = index;
ra->size = get_init_ra_size(req_size, max_pages);
- ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
+ ra->async_size = ra->size > req_size ? ra->size - req_size :
+ ra->size >> 1;
readit:
- /*
- * Will this read hit the readahead marker made by itself?
- * If so, trigger the readahead marker hit now, and merge
- * the resulted next readahead window into the current one.
- * Take care of maximum IO pages as above.
- */
- if (index == ra->start && ra->size == ra->async_size) {
- add_pages = get_next_ra_size(ra, max_pages);
- if (ra->size + add_pages <= max_pages) {
- ra->async_size = add_pages;
- ra->size += add_pages;
- } else {
- ra->size = max_pages;
- ra->async_size = max_pages >> 1;
- }
- }
-
ractl->_index = ra->start;
page_cache_ra_order(ractl, ra, order);
}
_
Patches currently in -mm which might be from jack@xxxxxxx are
revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
mm-avoid-overflows-in-dirty-throttling-logic.patch
readahead-make-sure-sync-readahead-reads-needed-page.patch
filemap-fix-page_cache_next_miss-when-no-hole-found.patch
readahead-properly-shorten-readahead-when-falling-back-to-do_page_cache_ra.patch
readahead-drop-pointless-index-from-force_page_cache_ra.patch
readahead-drop-index-argument-of-page_cache_async_readahead.patch
readahead-drop-dead-code-in-page_cache_ra_order.patch
readahead-drop-dead-code-in-ondemand_readahead.patch
readahead-disentangle-async-and-sync-readahead.patch
readahead-fold-try_context_readahead-into-its-single-caller.patch
readahead-simplify-gotos-in-page_cache_sync_ra.patch
