| Message ID | 20241108174505.1214230-4-axboe@kernel.dk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [01/13] mm/filemap: change filemap_create_folio() to take a struct kiocb | expand |
On Fri, Nov 08, 2024 at 10:43:26AM -0700, Jens Axboe wrote: > Add a page flag that file IO can use to indicate that the IO being done > is uncached, as in it should not persist in the page cache after the IO > has been completed. Flag bits are precious resource. It would be nice to re-use an existing bit if possible. PG_reclaim description looks suspiciously close to what you want. I wounder if it would be valid to re-define PG_reclaim behaviour to drop the page after writeback instead of moving to the tail of inactive list.
On 11/8/24 12:25 PM, Kirill A. Shutemov wrote: > On Fri, Nov 08, 2024 at 10:43:26AM -0700, Jens Axboe wrote: >> Add a page flag that file IO can use to indicate that the IO being done >> is uncached, as in it should not persist in the page cache after the IO >> has been completed. > > Flag bits are precious resource. It would be nice to re-use an existing > bit if possible. I knoew, like I mentioned in the reply to willy, I knew this one would be an interesting discussion in and of itself. > PG_reclaim description looks suspiciously close to what you want. > I wounder if it would be valid to re-define PG_reclaim behaviour to drop > the page after writeback instead of moving to the tail of inactive list. You're the mm expert - I added the flag since then it has a clearly defined meaning, and I would not need to worry about any kind of odd overlap in paths I didn't know about. Would definitely entertain reusing something else, but I'll leave that in the hands of the people that know this code and the various intricacies and assumptions a lot better than I do.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index cc839e4365c1..3c4003495929 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -110,6 +110,7 @@ enum pageflags { PG_reclaim, /* To be reclaimed asap */ PG_swapbacked, /* Page is backed by RAM/swap */ PG_unevictable, /* Page is "unevictable" */ + PG_uncached, /* uncached read/write IO */ #ifdef CONFIG_MMU PG_mlocked, /* Page is vma mlocked */ #endif @@ -562,6 +563,10 @@ PAGEFLAG(Reclaim, reclaim, PF_NO_TAIL) FOLIO_FLAG(readahead, FOLIO_HEAD_PAGE) FOLIO_TEST_CLEAR_FLAG(readahead, FOLIO_HEAD_PAGE) +FOLIO_FLAG(uncached, FOLIO_HEAD_PAGE) + FOLIO_TEST_CLEAR_FLAG(uncached, FOLIO_HEAD_PAGE) + __FOLIO_SET_FLAG(uncached, FOLIO_HEAD_PAGE) + #ifdef CONFIG_HIGHMEM /* * Must use a macro here due to header dependency issues. page_zone() is not diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index bb8a59c6caa2..b60057284102 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -116,7 +116,8 @@ DEF_PAGEFLAG_NAME(head), \ DEF_PAGEFLAG_NAME(reclaim), \ DEF_PAGEFLAG_NAME(swapbacked), \ - DEF_PAGEFLAG_NAME(unevictable) \ + DEF_PAGEFLAG_NAME(unevictable), \ + DEF_PAGEFLAG_NAME(uncached) \ IF_HAVE_PG_MLOCK(mlocked) \ IF_HAVE_PG_HWPOISON(hwpoison) \ IF_HAVE_PG_IDLE(idle) \
Add a page flag that file IO can use to indicate that the IO being done is uncached, as in it should not persist in the page cache after the IO has been completed. Signed-off-by: Jens Axboe <axboe@kernel.dk> --- include/linux/page-flags.h | 5 +++++ include/trace/events/mmflags.h | 3 ++- 2 files changed, 7 insertions(+), 1 deletion(-)