On Fri, 2021-10-01 at 07:11 -0400, David Wysochanski wrote: > > > On Fri, Sep 17, 2021 at 11:05 AM David Howells <dhowells@xxxxxxxxxx> > wrote: > > > > Move NFS to using the alternate fallback fscache I/O API instead of > > the old > > upstream I/O API as that is about to be deleted. The alternate API > > will > > also be deleted at some point in the future as it's dangerous (as > > is the > > old API) and can lead to data corruption if the backing filesystem > > can > > insert/remove bridging blocks of zeros into its extent list[1]. > > > > The alternate API reads and writes pages synchronously, with the > > intention > > of allowing removal of the operation management framework and > > thence the > > object management framework from fscache. > > > > The preferred change would be to use the netfs lib, but the new I/O > > API can > > be used directly. It's just that as the cache now needs to track > > data for > > itself, caching blocks may exceed page size... > > > > Changes > > ======= > > ver #2: > > - Changed "deprecated" to "fallback" in the new function > > names[2]. > > > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > > cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> > > cc: Anna Schumaker <anna.schumaker@xxxxxxxxxx> > > cc: linux-nfs@xxxxxxxxxxxxxxx > > cc: linux-cachefs@xxxxxxxxxx > > Link: https://lore.kernel.org/r/YO17ZNOcq+9PajfQ@xxxxxxx [1] > > Link: > > https://lore.kernel.org/r/CAHk-=wiVK+1CyEjW8u71zVPK8msea=qPpznX35gnX+s8sXnJTg@xxxxxxxxxxxxxx/ > > [2] > > Link: > > https://lore.kernel.org/r/163162771421.438332.11563297618174948818.stgit@xxxxxxxxxxxxxxxxxxxxxx/ > > # rfc > > --- > > > > fs/nfs/file.c | 14 +++-- > > fs/nfs/fscache.c | 161 +++++++----------------------------------- > > ------------ > > fs/nfs/fscache.h | 85 ++++------------------------- > > fs/nfs/read.c | 25 +++----- > > fs/nfs/write.c | 7 ++ > > 5 files changed, 55 insertions(+), 237 deletions(-) > > > > diff --git a/fs/nfs/file.c b/fs/nfs/file.c > > index aa353fd58240..209dac208477 100644 > > --- a/fs/nfs/file.c > > +++ b/fs/nfs/file.c > > @@ -416,7 +416,7 @@ static void nfs_invalidate_page(struct page > > *page, unsigned int offset, > > /* Cancel any unstarted writes on this page */ > > nfs_wb_page_cancel(page_file_mapping(page)->host, page); > > > > - nfs_fscache_invalidate_page(page, page->mapping->host); > > + wait_on_page_fscache(page); > > } > > > > /* > > @@ -432,7 +432,12 @@ static int nfs_release_page(struct page *page, > > gfp_t gfp) > > /* If PagePrivate() is set, then the page is not freeable > > */ > > if (PagePrivate(page)) > > return 0; > > - return nfs_fscache_release_page(page, gfp); > > + if (PageFsCache(page)) { > > + if (!(gfp & __GFP_DIRECT_RECLAIM) || !(gfp & > > __GFP_FS)) > > + return false; > > + wait_on_page_fscache(page); > > + } I've found this generally not to be safe. The VM calls ->release_page() from a variety of contexts, and often fails to report it correctly in the gfp flags. That's particularly true of the stuff in mm/vmscan.c. This is why we have the check above that vetos page removal upon PagePrivate() being set. > -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
