mmotm - unevictable lru/mlocked pages fixes/cleanup

Here are a set of fixes and cleanup to the unevictable lru and mlocked pages patches against 27-rc1+mmotm-080730-0356. In addition to the patches, I have a few suggestions for fixing up a few patch descriptions, and other potential cleanups, below.

The following patch names are the file names I'm using in my tree. The names indicate where in the series the patch goes. I've also mentioned in the patch descriptions which patch each one fixes.

unevictable-lru-infrastructure-putback-fix1.patch

I noticed that putback_lru_page() would forget the active state of a page in the event of a "redo". [Note: I added a vm event to record any redos. I've never seen any redos in any of my stress testing since Kamezawa-san reworked putback_lru_pages().] This patch remembers the page's incoming PageActive state. Not sure this is required.

Can be folded with unevictable-lru-infrastructure.patch

unevictable-lru-infrastructure-putback-fix2.patch

Remove the unevictable page vm event counting from putback_lru_page(), as this breaks a bisect. The necessary vmstat events have not been defined until later in the series. Subsequent patches will add back in the event counting at appropriate places

Can be folded with unevictable-lru-infrastructure.patch

unevictable-lru-page-statistics-add-events.patch

Define the vmstat events for the unevictable lru infrastructure and count them here, separately from the mlocked pages stats.

Renames the NORECL/noreclaim vmstat events to UNEVICTABLE/unevictable ...

This patch may be folded with the
unevictable-lru-page-statistics.patch

shm_locked-pages-are-unevictable-add-vm-events.patch

Add unevictable lru event counting to scan of the unevictable lru list[s] for a mapping's pages. May be folded with shm_locked-pages-are-unevictable.patch

vmstat-mlocked-pages-statistics-add-vm-events.patch

Add mlocked pages related vm event definitions and counting. May be folded with vmstat-mlocked-pages-statistics.patch

mlock-count-attempts-to-free-mlocked-page.patch

REPLACE the existing patch of this name with this one. It resolves patch conflicts resulting from the renaming of the events and handles the renaming in unconflicted hunks.

vmstat-unevictable-and-mlocked-pages-vm-events.patch

REMOVE this patch from the series. It is superceeded by the preceeding patches that define the vm events with the appropriate statistics patch.

Other notes and patch description updates:

1) Kosaki-san's munlock rework patch [removal of page table walker] has been folded with:
mmap-handle-mlocked-pages-during-map-remap-unmap.patch
Technically, it should be part of:
mlock-mlocked-pages-are-unevictable.patch
where it would have just removed/replaced the patch chunks that added the page table walker.

2) Patch description of ramfs-and-ram-disk-pages-are-unevictable.patch is stale, since the brd driver replaced rd--ram disk pages are no longer on the lru. I'll send a suggested replacement description as part of this series.

3) Since the putback_lru_page() rework, the patch description of shm_locked-pages-are-unevictable.patch is stale. Suggest:

Remove the text from the last paragraph of the description, starting with:
"Note that scan_mapping_unevictable_page() must be able to sleep..."

4) Kosaki-san's munlock rework obsolete's note 5 in the description for mlock-mlocked-pages-are-unevictable.patch.

Could just make a note to this effect with the folded "introduce __get_user_pages()" patch description.

5) The putback_lru_page() and munlock() rework requires update of the unevictable-lru.txt in Documentation. I'll send an update patch [later].

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