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mm: reference totalram_pages and managed_pages once per function

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Patch series "mm: convert totalram_pages, totalhigh_pages and managed
pages to atomic", v5.

This series converts totalram_pages, totalhigh_pages and
zone->managed_pages to atomic variables.

totalram_pages, zone->managed_pages and totalhigh_pages updates are
protected by managed_page_count_lock, but readers never care about it.
Convert these variables to atomic to avoid readers potentially seeing a
store tear.

Main motivation was that managed_page_count_lock handling was complicating
things.  It was discussed in length here,
https://lore.kernel.org/patchwork/patch/995739/#1181785 It seemes better
to remove the lock and convert variables to atomic.  With the change,
preventing poteintial store-to-read tearing comes as a bonus.

This patch (of 4):

This is in preparation to a later patch which converts totalram_pages and
zone->managed_pages to atomic variables.  Please note that re-reading the
value might lead to a different value and as such it could lead to
unexpected behavior.  There are no known bugs as a result of the current
code but it is better to prevent from them in principle.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arun KS <[email protected]>
Reviewed-by: Konstantin Khlebnikov <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: Pavel Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Arun KS 2018-12-28 00:34:20 -08:00 • committed by Linus Torvalds
commit 3d6357de8a
12 changed files with 44 additions and 33 deletions
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19
drivers/hv/hv_balloon.c
View file

@ -1090,6 +1090,7 @@ static void process_info(struct hv_dynmem_device *dm, struct dm_info_msg *msg)
static unsigned long compute_balloon_floor(void)
{
unsigned long min_pages;
unsigned long nr_pages = totalram_pages;
#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
/* Simple continuous piecewiese linear function:
* max MiB -> min MiB gradient
@ -1102,16 +1103,16 @@ static unsigned long compute_balloon_floor(void)
* 8192 744 (1/16)
* 32768 1512 (1/32)
*/
if (totalram_pages < MB2PAGES(128))
min_pages = MB2PAGES(8) + (totalram_pages >> 1);
else if (totalram_pages < MB2PAGES(512))
min_pages = MB2PAGES(40) + (totalram_pages >> 2);
else if (totalram_pages < MB2PAGES(2048))
min_pages = MB2PAGES(104) + (totalram_pages >> 3);
else if (totalram_pages < MB2PAGES(8192))
min_pages = MB2PAGES(232) + (totalram_pages >> 4);
if (nr_pages < MB2PAGES(128))
min_pages = MB2PAGES(8) + (nr_pages >> 1);
else if (nr_pages < MB2PAGES(512))
min_pages = MB2PAGES(40) + (nr_pages >> 2);
else if (nr_pages < MB2PAGES(2048))
min_pages = MB2PAGES(104) + (nr_pages >> 3);
else if (nr_pages < MB2PAGES(8192))
min_pages = MB2PAGES(232) + (nr_pages >> 4);
else
min_pages = MB2PAGES(488) + (totalram_pages >> 5);
min_pages = MB2PAGES(488) + (nr_pages >> 5);
#undef MB2PAGES
return min_pages;
}