fadvise NOREUSE and fadvise DONTNEED *twice*

There is a promising patch that adds POSIX_FADV_NOREUSE heuristics, see http://article.gmane.org/gmane.linux.kernel.mm/65564 > This will mean that there is no way currently to > remove a particular file from the cache on linux. Correct. There's not a way to do this for a single file (except running POSIX_FADV_DONTNEED twice...). If only one fadvise64 syscall is performed, the *first* previously unsused page will somehow not be forgotten.

fadvise NOREUSE and fadvise DONTNEED twice
db0b9fb1 · Julius Plenz · 43c71e1a · db0b9fb1 · db0b9fb1
Commit db0b9fb1 authored Feb 04, 2012 by Julius Plenz
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fcntl_helpers.c fcntl_helpers.c +5 -0

nocache.c nocache.c +3 -0

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--- a/fcntl_helpers.c
+++ b/fcntl_helpers.c
@@ -9,6 +9,11 @@ int fadv_dontneed(int fd, off_t offset, off_t len)
        return posix_fadvise(fd, offset, len, POSIX_FADV_DONTNEED);
 }

+int fadv_noreuse(int fd, off_t offset, off_t len)
+{
+        return posix_fadvise(fd, offset, len, POSIX_FADV_NOREUSE);
+}
+
 void sync_if_writable(int fd)
 {
    int r;

--- a/nocache.c
+++ b/nocache.c
@@ -19,6 +19,7 @@ int close(int fd);
 static void store_pageinfo(int fd);
 static void free_unclaimed_pages(int fd);
 extern int fadv_dontneed(int fd, off_t offset, off_t len);
+extern int fadv_noreuse(int fd, off_t offset, off_t len);
 extern void sync_if_writable(int fd);

 #define _MAX_FDS 1024
@@ -51,6 +52,7 @@ int open(const char *pathname, int flags, mode_t mode)
    if((fd = _original_open(pathname, flags, mode)) != -1) {
        pthread_mutex_lock(&lock);
        store_pageinfo(fd);
+        fadv_noreuse(fd, 0, 0);
        pthread_mutex_unlock(&lock);
    }
    return fd;
@@ -155,6 +157,7 @@ static void free_unclaimed_pages(int fd)
    for(j = 0; j < fds[i].nr_pages; j++) {
        if(!(fds[i].info[j] & 1)) {
            fadv_dontneed(fd, j*PAGESIZE, PAGESIZE);
+            fadv_dontneed(fd, j*PAGESIZE, PAGESIZE);
        }
    }