| Message ID | 20241213155557.105419-5-axboe@kernel.dk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Uncached buffered IO | expand |
On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: > Add a folio flag that file IO can use to indicate that the cached IO > being done should be dropped from the page cache upon completion. > > Signed-off-by: Jens Axboe <axboe@kernel.dk> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> + David, Vlastimil. I think we should consider converting existing folio_set_reclaim() / SetPageReclaim() users to the new flag. From a quick scan, all of them would benefit from dropping the page after writeback is complete instead of leaving the folio on the LRU.
On Fri, Dec 20, 2024 at 01:08:39PM +0200, Kirill A. Shutemov wrote: > On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: > > Add a folio flag that file IO can use to indicate that the cached IO > > being done should be dropped from the page cache upon completion. > > > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > + David, Vlastimil. > > I think we should consider converting existing folio_set_reclaim() / > SetPageReclaim() users to the new flag. From a quick scan, all of them > would benefit from dropping the page after writeback is complete instead > of leaving the folio on the LRU. Ooh, that would be nice. Removes the overloading of PG_reclaim with PG_readahead, right?
On 20.12.24 12:08, Kirill A. Shutemov wrote: > On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: >> Add a folio flag that file IO can use to indicate that the cached IO >> being done should be dropped from the page cache upon completion. >> >> Signed-off-by: Jens Axboe <axboe@kernel.dk> > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > + David, Vlastimil. > > I think we should consider converting existing folio_set_reclaim() / > SetPageReclaim() users to the new flag. From a quick scan, all of them > would benefit from dropping the page after writeback is complete instead > of leaving the folio on the LRU. I wonder of there are some use cases where we write a lot of data to then only consume it read-only from that point on (databases? fancy AI stuff? no idea :) ).
On Fri, Dec 20, 2024 at 02:38:09PM +0000, Matthew Wilcox wrote: > On Fri, Dec 20, 2024 at 01:08:39PM +0200, Kirill A. Shutemov wrote: > > On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: > > > Add a folio flag that file IO can use to indicate that the cached IO > > > being done should be dropped from the page cache upon completion. > > > > > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > > > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > > > + David, Vlastimil. > > > > I think we should consider converting existing folio_set_reclaim() / > > SetPageReclaim() users to the new flag. From a quick scan, all of them > > would benefit from dropping the page after writeback is complete instead > > of leaving the folio on the LRU. > > Ooh, that would be nice. Removes the overloading of PG_reclaim with > PG_readahead, right? Yep.
On Fri, Dec 20, 2024 at 04:03:44PM +0100, David Hildenbrand wrote: > On 20.12.24 12:08, Kirill A. Shutemov wrote: > > On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: > > > Add a folio flag that file IO can use to indicate that the cached IO > > > being done should be dropped from the page cache upon completion. > > > > > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > > > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > > > + David, Vlastimil. > > > > I think we should consider converting existing folio_set_reclaim() / > > SetPageReclaim() users to the new flag. From a quick scan, all of them > > would benefit from dropping the page after writeback is complete instead > > of leaving the folio on the LRU. > > I wonder of there are some use cases where we write a lot of data to then > only consume it read-only from that point on (databases? fancy AI stuff? no > idea :) ). Do we use PG_reclaim for such cases?
On 20.12.24 16:12, Kirill A. Shutemov wrote: > On Fri, Dec 20, 2024 at 04:03:44PM +0100, David Hildenbrand wrote: >> On 20.12.24 12:08, Kirill A. Shutemov wrote: >>> On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: >>>> Add a folio flag that file IO can use to indicate that the cached IO >>>> being done should be dropped from the page cache upon completion. >>>> >>>> Signed-off-by: Jens Axboe <axboe@kernel.dk> >>> >>> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> >>> >>> + David, Vlastimil. >>> >>> I think we should consider converting existing folio_set_reclaim() / >>> SetPageReclaim() users to the new flag. From a quick scan, all of them >>> would benefit from dropping the page after writeback is complete instead >>> of leaving the folio on the LRU. >> >> I wonder of there are some use cases where we write a lot of data to then >> only consume it read-only from that point on (databases? fancy AI stuff? no >> idea :) ). > > Do we use PG_reclaim for such cases? Good point, I looked at the pageout() case, but there we really want to pageout that thing and not just write it back, so makes sense to me.
On Fri, Dec 20, 2024 at 05:11:52PM +0200, Kirill A. Shutemov wrote: > On Fri, Dec 20, 2024 at 02:38:09PM +0000, Matthew Wilcox wrote: > > On Fri, Dec 20, 2024 at 01:08:39PM +0200, Kirill A. Shutemov wrote: > > > On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote: > > > > Add a folio flag that file IO can use to indicate that the cached IO > > > > being done should be dropped from the page cache upon completion. > > > > > > > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > > > > > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > > > > > + David, Vlastimil. > > > > > > I think we should consider converting existing folio_set_reclaim() / > > > SetPageReclaim() users to the new flag. From a quick scan, all of them > > > would benefit from dropping the page after writeback is complete instead > > > of leaving the folio on the LRU. > > > > Ooh, that would be nice. Removes the overloading of PG_reclaim with > > PG_readahead, right? > > Yep. Then ... maybe this series should just coopt the PG_reclaim flag for its purposes? Going through the users: lru_deactivate_file() --------------------- Called due to mapping_try_invalidate() failing to invalidate. Absolutely, get rid of this folio as quickly as possible. pageout() --------- Again, we're trying to get rid of this folio. This time due to memory pressure / reaching the end of the LRU list. Yup, we want it gone. shrink_folio_list() ------------------- Again, end of the LRU (both cases in this function) zswap_writeback_entry() ----------------------- This is exactly the same case that Jens is adding. The swapcache is being used as a staging location, and we want the folio gone as soon as writeback completes.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index cf46ac720802..16607f02abd0 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_dropbehind, /* drop pages on IO completion */ #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(dropbehind, FOLIO_HEAD_PAGE) + FOLIO_TEST_CLEAR_FLAG(dropbehind, FOLIO_HEAD_PAGE) + __FOLIO_SET_FLAG(dropbehind, 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..3bc8656c8359 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(dropbehind) \ IF_HAVE_PG_MLOCK(mlocked) \ IF_HAVE_PG_HWPOISON(hwpoison) \ IF_HAVE_PG_IDLE(idle) \
Add a folio flag that file IO can use to indicate that the cached IO being done should be dropped from the page cache upon completion. 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(-)