Explicit Flush of Deferred Writes¶
An explicit storage-layer operation that selects earlier deferred writes and establishes a documented transfer, cache-flush, or ordering boundary for that set.
Core Idea¶
An explicit flush of deferred writes asks one storage layer to advance a defined set of earlier writes that may still be in volatile state. To understand the result, name the layer, the earlier set, the operation, and the effect that the interface actually promises. The word “flush” alone does not tell us that every cache or file name is safe against a crash.
For a Linux file, fsync(fd) transfers the file's modified data and metadata and waits for the storage device to report completion; a caller can check its success or error result.[1] At a different layer, a pure block preflush request flushes previously completed writes in a block device's volatile cache without a dependent new write.[2] Linux names the block flag REQ_PREFLUSH.[2] These are two documented storage interfaces with a shared earlier-write-set structure, not identical commands or measured device behavior.
Scope of Application¶
Use this entry when a storage interface identifies earlier writes and provides an explicit request to advance them across its stated boundary. The two cases here are Linux file synchronization and a Linux block-device cache preflush. Linux syncfs is broader than fsync: it synchronizes pending data and metadata for the filesystem containing its file descriptor.[1][3]
The Linux sync call waits for I/O, but its void return gives no per-call writeback-error result; POSIX only requires scheduling before return.[3] A file fsync also does not necessarily synchronize the directory entry that names the file; when that name matters, the containing directory must be synchronized separately.[1] A device preflush does not include host pages that have not been submitted or device writes that have not completed.[2]
Clarity¶
Ask: Which storage layer? Which earlier writes? Which request? Which completion or ordering claim?
A file's modified in-core data and a drive's already-completed but cached writes are different sets.[1][2] A successful fsync gives a checkable file-level result and device-reported transfer, subject to the manual's filesystem and device-cache caveats.[1] The cited block-layer description specifies the pure cache-flush effect but does not supply an fsync-like user-visible return contract for its helper.[2]
Manages Complexity¶
A write may pass through several layers before it reaches nonvolatile storage. Identify the layer relevant to the application's dependency, then check that layer's eligible earlier set and documented result. If the application also needs a newly created file name, file-only fsync leaves a directory-entry question to resolve.[1] If the concern is a device's volatile cache, a pure preflush concerns previously completed device writes, not writes still waiting in host memory.[2] This keeps one operation's scope from being silently substituted for another's.
Abstract Reasoning¶
The structure is named layer → earlier vulnerable set → explicit request → bounded effect. In the file case, the set is modified data and metadata of a selected file and the request is fsync(fd).[1] In the block case, the set is previously completed writes held in a volatile device cache and the request is an otherwise empty preflush.[2]
If an operation only forces a new flagged write, it does not by itself satisfy the earlier-set test. Linux REQ_FUA governs completion of the flagged current write, whereas REQ_PREFLUSH addresses the prior completed device-cache set.[2] The entry presupposes a Boundary: the interface must define what belongs to the selected volatile set and what effect counts as crossing it. That is a strict prerequisite relation to Boundary, not a claim that this procedure is a kind of boundary.
Knowledge Transfer¶
The four questions transfer between file and device interfaces, but their answers change. fsync concerns one file and has a status result; a pure block preflush concerns previously completed device writes and the cited kernel description does not give its helper an equivalent user-facing return rule.[1][2] Calling an unrelated output-buffer operation a “flush” is only a vocabulary analogy until its eligible set and effect are established. The selected identity remains storage-specific.
Relationships to Other Abstractions¶
Current abstraction Explicit Flush of Deferred Writes Domain-specific
Parents (1) — outgoing typed relations
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Explicit Flush of Deferred Writes presupposes Boundary Prime
The selected prior-write flush presupposes an operative storage-layer boundary that defines the eligible volatile set and its documented post-transfer or post-flush state.
Hierarchy path (1) — routes to 1 parentless root
- Explicit Flush of Deferred Writes → presupposes Boundary
Neighborhood in Abstraction Space¶
Explicit Flush of Deferred Writes sits in a sparse region of the domain-specific corpus (94th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.
Family — Unclustered & Miscellaneous (2769 abstractions)
Nearest neighbors
- Memory Corruption — 0.79
- Cache Inclusion Policy — 0.78
- No-Force Policy — 0.78
- Runahead Execution — 0.77
- Checkpoint and restore — 0.77
Computed from structural-signature embeddings · 2026-10-25
References¶
[1] Linux man-pages project. “fsync(2), fdatasync(2) — synchronize a file's in-core state with storage device,” Linux man-pages 6.19 (8 February 2026), DESCRIPTION, RETURN VALUE, and HISTORY. https://man7.org/linux/man-pages/man2/fsync.2.html. Documents file-data and metadata scope, directory-entry qualification, device-reported completion, return status, and older-kernel/filesystem cache limits. registry ↩a ↩b ↩c ↩d ↩e ↩f ↩g ↩h
[2] Linux kernel documentation. “Explicit volatile write back cache control,” Introduction, Explicit cache flushes, and Forced Unit Access. https://docs.kernel.org/block/writeback_cache_control.html. Defines volatile device write-cache behavior, pure and attached preflush requests, and forced-unit-access behavior. registry ↩a ↩b ↩c ↩d ↩e ↩f ↩g ↩h ↩i
[3] Linux man-pages project. “sync(2), syncfs(2) — commit filesystem caches to disk,” Linux man-pages 6.19 (8 February 2026), DESCRIPTION, RETURN VALUE, ERRORS, VERSIONS, and HISTORY. https://man7.org/linux/man-pages/man2/sync.2.html. Distinguishes Linux sync, syncfs, POSIX scheduling, and Linux 5.8 writeback-error reporting. registry ↩a ↩b