From: Junio C Hamano Date: Wed, 09 Mar 2022 23:48:06 GMT Subject: Re: [PATCH v5 2/5] core.fsyncmethod: add writeout-only mode Message-ID: In-Reply-To: "Neeraj Singh via GitGitGadget" writes: > From: Neeraj Singh > > This commit introduces the `core.fsyncMethod` configuration > knob, which can currently be set to `fsync` or `writeout-only`. > > The new writeout-only mode attempts to tell the operating system to > flush its in-memory page cache to the storage hardware without issuing a > CACHE_FLUSH command to the storage controller. > > Writeout-only fsync is significantly faster than a vanilla fsync on > common hardware, since data is written to a disk-side cache rather than > all the way to a durable medium. Later changes in this patch series will > take advantage of this primitive to implement batching of hardware > flushes. > > When git_fsync is called with FSYNC_WRITEOUT_ONLY, it may fail and the > caller is expected to do an ordinary fsync as needed. > > On Apple platforms, the fsync system call does not issue a CACHE_FLUSH > directive to the storage controller. This change updates fsync to do > fcntl(F_FULLFSYNC) to make fsync actually durable. We maintain parity > with existing behavior on Apple platforms by setting the default value > of the new core.fsyncMethod option. > > Signed-off-by: Neeraj Singh > --- OK. This seems to be quite reasonable in that the pieces of code that use fsync_or_die() do not have to change at all, and all of them will keep behaving the same way. In other words, the "how" of fsync is very much well isolated. Nice.